



Internet Engineering Task Force (IETF)                    M. Koster, Ed.
Request for Comments: 9880                                KTC Control AB
Category: Standards Track                                C. Bormann, Ed.
ISSN: 2070-1721                                   Universität Bremen TZI
                                                              A. Keränen
                                                                Ericsson
                                                            January 2026


  Semantic Definition Format (SDF) for Data and Interactions of Things

Abstract

   The Semantic Definition Format (SDF) is a format for domain experts
   to use in the creation and maintenance of data and interaction models
   that describe Things, i.e., physical objects that are available for
   interaction over a network.  An SDF specification describes
   definitions of SDF Objects/SDF Things and their associated
   interactions (Events, Actions, and Properties), as well as the Data
   types for the information exchanged in those interactions.  Tools
   convert this format to database formats and other serializations as
   needed.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9880.

Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Structure of This Document
     1.2.  Terminology and Conventions
       1.2.1.  Programming Platform Terms
       1.2.2.  Conceptual Terms
       1.2.3.  Specification Language Terms
       1.2.4.  Conventions
   2.  Overview
     2.1.  Example Definition
     2.2.  Elements of an SDF Model
       2.2.1.  sdfObject
       2.2.2.  sdfProperty
       2.2.3.  sdfAction
       2.2.4.  sdfEvent
       2.2.5.  sdfData
       2.2.6.  sdfThing
     2.3.  Member Names: Given Names and Quality Names
       2.3.1.  Given Names and Quality Names
       2.3.2.  Hierarchical Names
       2.3.3.  Extensibility of Given Names and Quality Names
   3.  SDF Structure
     3.1.  Information Block
     3.2.  Namespaces Block
     3.3.  Definitions Block
     3.4.  Top-Level Affordances and sdfData
   4.  Names and Namespaces
     4.1.  Structure
     4.2.  Contributing Global Names
     4.3.  Referencing Global Names
     4.4.  sdfRef
       4.4.1.  Resolved Models
     4.5.  sdfRequired
     4.6.  Common Qualities
     4.7.  Data Qualities
       4.7.1.  sdfType
       4.7.2.  sdfChoice
   5.  Keywords for Definition Groups
     5.1.  sdfObject
     5.2.  sdfProperty
     5.3.  sdfAction
     5.4.  sdfEvent
     5.5.  sdfData
   6.  High-Level Composition
     6.1.  Paths in the Model Namespaces
     6.2.  Modular Composition
       6.2.1.  Use of the "sdfRef" Keyword to Reuse a Definition
     6.3.  sdfThing
   7.  IANA Considerations
     7.1.  Media Type
     7.2.  Content-Format
     7.3.  IETF URN Sub-Namespace for Unit Names
           (urn:ietf:params:unit)
     7.4.  SenML Registry Group
     7.5.  Registries
       7.5.1.  SDF Quality Names
       7.5.2.  SDF Quality Name Prefixes
       7.5.3.  sdfType Values
       7.5.4.  SDF Feature Names
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Appendix A.  Formal Syntax of SDF
   Appendix B.  json-schema.org Rendition of SDF Syntax
   Appendix C.  Data Qualities Inspired by json-schema.org
     C.1.  type "number", type "integer"
     C.2.  type "string"
     C.3.  type "boolean"
     C.4.  type "array"
     C.5.  type "object"
     C.6.  Implementation Notes
   Appendix D.  Composition Examples
     D.1.  Outlet Strip Example
     D.2.  Refrigerator-Freezer Example
   Appendix E.  Some Changes from Earlier Draft Versions of this
           Specification
   List of Figures
   List of Tables
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   The Semantic Definition Format (SDF) is concerned with Things, namely
   physical objects that are available for interaction over a network.
   SDF is a format for domain experts to use in the creation and
   maintenance of data and interaction models that describe Things.  An
   SDF specification describes definitions of SDF Objects/SDF Things and
   their associated interactions (Events, Actions, and Properties), as
   well as the Data types for the information exchanged in those
   interactions.  Tools convert this format to database formats and
   other serializations as needed.

   SDF is designed to be an extensible format.  The present document
   constitutes the base specification for SDF, "base SDF" for short.  In
   addition, SDF extensions can be defined, some of which may make use
   of extension points specifically defined for this in base SDF.  One
   area for such extensions would be refinements of SDF's abstract
   interaction models into protocol bindings for specific ecosystems
   (e.g., [SDF-MAPPING]).  For the use of certain other extensions, it
   may be necessary to indicate in the SDF document using them that a
   specific extension is in effect; see Section 3.1 for details of the
   features quality that can be used for such indications.  With
   extension points and feature indications available, base SDF does not
   define a "version" concept for the SDF format itself (as opposed to
   version indications within SDF documents indicating their own
   evolution; see Section 3.1).

1.1.  Structure of This Document

   After introductory material and an overview (Section 2) over the
   elements of the model and the different kinds of names used,
   Section 3 introduces the main components of an SDF model.  Section 4
   revisits names and structures them into namespaces.  Section 5
   discusses the inner structure of the Objects defined by SDF, the
   sdfObjects, in further detail.  Section 6 discusses how SDF supports
   composition.  Conventional Sections (IANA Considerations, Security
   Considerations, Normative References, and Informative References)
   follow.  The normative Appendix A defines the syntax of SDF in terms
   of its JSON structures, employing the Concise Data Definition
   Language (CDDL) [RFC8610].  This is followed by the informative
   Appendix B, a rendition of the SDF syntax in a "JSON Schema" format
   as they are defined by json-schema.org (collectively called JSO).
   The normative Appendix C defines certain terms ("data qualities")
   used at the SDF data model level that were inspired by JSO.  The
   informative Appendix D provides a few examples for the use of
   composition in SDF.  Finally, Appendix E provides some historical
   information that can be useful in upgrading earlier, pre-standard SDF
   models and implementations to base SDF.

1.2.  Terminology and Conventions

   Terms introduced in this section are capitalized when used in this
   section.  To maintain readability, capitalization is only used when
   needed where they are used in the body of this document.

1.2.1.  Programming Platform Terms

   The following definitions mention terms that are used with specific
   meanings in various programming platforms, but often have an
   independent definition for this document, which can be found further
   below in this section.

   Element:  A generic term used here in its English sense.
      Exceptionally, in Appendix C, the term is used explicitly in
      accordance with its meaning in the JSON ecosystem, i.e., the
      elements of JSON arrays.

   Entry:  A key-value pair in a map.  (In JSON maps, sometimes also
      called "member".)

   Map:  A collection of entries (key-value pairs) where there are no
      two entries with equivalent keys.  (Also known as associative
      array, dictionary, or symbol table.)

   Object:  An otherwise very generic term that JavaScript (and thus
      JSON) uses for the kind of maps that were part of the original
      languages from the outset.  In this document, Object is used
      exclusively in its general English meaning or as the colloquial
      shorthand for sdfObject, even if the type name "object" is
      imported with JSON-related semantics from a data definition
      language.

   Property:  Certain environments use the term "property" for a JSON
      concept that JSON calls "member" and is called "entry" here, or
      sometimes just for the map key of these.  In this document, the
      term Property is specifically reserved for a certain kind of
      Affordance, even if the map key "properties" is imported with
      JSON-related semantics from a data definition language.

   Byte:  This document uses the term "byte" in its now-customary sense
      as a synonym for "octet".

1.2.2.  Conceptual Terms

   Thing:  A physical item that is also available for interaction over a
      network.

   Element:  A part or an aspect of something abstract; i.e., the term
      is used here in its usual English definition.

   Affordance:  An element of an interface offered for interaction.
      Such an element becomes an Affordance when information is
      available (directly or indirectly) that indicates how it can or
      should be used.  In the present document, the term is used for the
      digital (network-directed) interfaces of a Thing only; as it is a
      physical object as well, the Thing might also have physical
      affordances such as buttons, dials, and displays.  The
      specification language offers certain ways to create sets of
      related Affordances and combine them into "Groupings" (see below).

   Property:  An Affordance that can potentially be used to read, write,
      and/or observe state (current/stored information) on a Grouping.

   Action:  An Affordance that can potentially be used to perform a
      named operation on a Grouping.

   Event:  An Affordance that can potentially be used to obtain
      information about what happened to a Grouping.

1.2.3.  Specification Language Terms

   SDF Document:  Container for SDF Definitions, together with data
      about the SDF Document itself (information block).  Represented as
      a JSON text representing a single JSON map, which is built from
      nested maps.

   SDF Model:  Definitions and declarations that model the digital
      interaction opportunities offered by one or more kinds of Things,
      represented by Groupings (sdfObjects and sdfThings).  An SDF Model
      can be fully contained in a single SDF Document, or it can be
      built from an SDF Document that references definitions and
      declarations from additional SDF documents.  The term SDF
      Specification can be used when the distinction between the
      distribution into individual SDF Documents and the abstract nature
      of the SDF Model is not of interest.

   Block:  One or more entries in a JSON map that is part of an SDF
      specification.  These entries can be described as a Block to
      emphasize that they serve a specific function together.

   Group:  An entry in the top-level JSON map that represents the SDF
      document.  Groups also can be used in certain nested definitions.
      A group has a Class Name Keyword as its key and a map of named
      definition entries (Definition Group) as a value.

   Class Name Keyword:  One of sdfThing, sdfObject, sdfProperty,
      sdfAction, sdfEvent, or sdfData.  The Classes for these type
      keywords are capitalized and prefixed with sdf.

   Class:  Abstract term for the information that is contained in groups
      identified by a Class Name Keyword.

   Quality:  A metadata item in a definition or declaration that says
      something about that definition or declaration.  A quality is
      represented in SDF as an entry in a JSON map (JSON object) that
      serves as a definition or declaration.  (The term "Quality" is
      used because another popular term, "Property", already has a
      different meaning.)

   Definition:  An entry in a Definition Group.  The entry creates a new
      semantic term for use in SDF models and associates it with a set
      of qualities.  Unless the Class Name Keyword of the Group also
      makes it a Declaration (see Section 3.3), a definition just
      defines a term and it does not create a component item within the
      enclosing definition.

   Declaration:  A definition within an enclosing definition that is
      intended to create a component item within that enclosing
      definition.  Every declaration can also be used as a definition
      for reference elsewhere.

   Grouping:  An sdfThing or sdfObject, i.e., (directly or indirectly) a
      description for a combination of Affordances.

   Object, sdfObject:  A Grouping where the declarations that it
      contains are for Affordances only (Property, Action, and Event
      declarations).  It serves as the main "atom" of reusable semantics
      for model construction, representing the interaction model for a
      Thing that is simple enough to not require a nested structure.
      Therefore, sdfObjects are similar to sdfThings, but do not allow
      nesting, i.e., they cannot contain other Groupings (sdfObjects or
      sdfThings).

   sdfThing:  A Grouping that can contain nested Groupings (sdfThings
      and sdfObjects).  Like sdfObject, it can also contain Affordance
      declarations (Property, Action, and Event declarations).  (Note
      that "Thing" has a different meaning from sdfThing and is
      therefore not available as a colloquial shorthand of sdfThing.)

   Augmentation Mechanism:  A companion document to a base SDF Model
      that provides additional information ("augments" the base
      specification).  The information may be for use in a specific
      ecosystem or with a specific protocol ("Protocol Binding").  No
      specific Augmentation Mechanisms are defined in base SDF.  A
      simple mechanism for such augmentations has been discussed as a
      "mapping file" [SDF-MAPPING].

   Protocol Binding:  A companion document to an SDF Model that defines
      how to map the abstract concepts in the model into the protocols
      that are in use in a specific ecosystem.  The Protocol Binding
      might supply URL components, numeric IDs, and similar details.
      Protocol Bindings are one case of an Augmentation Mechanism.

1.2.4.  Conventions

   Regular expressions that are used in the text as a "pattern" for some
   string are interpreted as per [RFC9485].  (Note that a form of
   regular expressions is also used as values of the quality pattern;
   see Appendix C.2.)

   The term "URI" in this document always refers to "full" URIs ("URI"
   in Section 3 of RFC 3986 [STD66]), never to relative URI references
   ("relative-ref" in Section 4.1 of RFC 3986 [STD66]), so the term
   "URI" does _NOT_ serve as the colloquial abbreviation of "URI-
   Reference" it is often used for.  Therefore, the "reference
   resolution" process defined in Section 5 of RFC 3986 [STD66] is _NOT_
   used in this specification.  Where necessary, full URIs are assembled
   out of substrings by simple concatenation, e.g., when CURIEs are
   expanded (Section 4.3) or when a global name is formed out of a
   namespace absolute-URI (Section 5 of RFC 3986 [STD66]) and a fragment
   identifier part (Section 4.1).  Also note that URIs are not only used
   to construct the SDF models, they are also the _subject_ of SDF
   models where they are used as data in actual interactions (and could
   even be represented as relative references there); these two usages
   are entirely separate.

   The singular form is chosen as the preferred one for the keywords
   defined in this specification.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Overview

2.1.  Example Definition

   The overview starts with an example for the SDF definition of a
   simple sdfObject called "Switch" (Figure 1).

   {
     "info": {
       "title": "Example document for SDF (Semantic Definition Format)",
       "version": "2019-04-24",
       "copyright": "Copyright 2019 Example Corp. All rights reserved.",
       "license": "https://example.com/license"
     },
     "namespace": {
       "cap": "https://example.com/capability/cap"
     },
     "defaultNamespace": "cap",
     "sdfObject": {
       "Switch": {
         "sdfProperty": {
           "value": {
             "description":
   "The state of the switch; false for off and true for on.",
             "type": "boolean"
           }
         },
         "sdfAction": {
           "on": {
             "description":
   "Turn the switch on; equivalent to setting value to true."
           },
           "off": {
             "description":
   "Turn the switch off; equivalent to setting value to false."
           },
           "toggle": {
             "description":
   "Toggle the switch; equivalent to setting value to its complement."
           }
         }
       }
     }
   }

               Figure 1: A Simple Example of an SDF Document

   This is a model of a switch.  The state value declared in the
   sdfProperty group, represented by a Boolean, will be true for "on"
   and will be false for "off".  The Actions on or off declared in the
   sdfAction group are redundant with setting the value and are in the
   example to illustrate that there are often different ways of
   achieving the same effect.  The action toggle will invert the value
   of the sdfProperty value so that 2-way switches can be created;
   having such action will avoid the need for retrieving the current
   value first and then applying/setting the inverted value.

   The sdfObject group lists the affordances of Things modeled by this
   sdfObject.  The sdfProperty group lists the Property affordances
   described by the model; these represent various perspectives on the
   state of the sdfObject.  Properties can have additional qualities to
   describe the state more precisely.  Properties can be annotated to be
   read, write, or read/write; how this is actually done by the
   underlying transfer protocols is not described in the SDF model but
   left to companion protocol bindings.  Properties are often used with
   RESTful paradigms [REST-IOT] describing state.  The sdfAction group
   is the mechanism to describe other interactions in terms of their
   names, input, and output data (no data are used in the example), as
   in a POST method in REST or in a remote procedure call.  The example
   toggle is an Action that changes the state based on the current state
   of the Property named value.  (The third type of affordance is
   Events, which are not described in this example.)

   In the JSON representation, the info group is an exception in that
   this group's map has keys taken from the SDF vocabulary.  All other
   groups (such as namespace and sdfObject) have maps with keys that are
   freely defined by the model writer (Switch, value, on, etc.).  These
   map keys are therefore called _Given Names_. The groups made up of
   entries with Given Names as keys usually use the named<> production
   in the formal syntax of SDF (Appendix A).  Where the values of these
   entries are maps, these again use SDF vocabulary keys, and so on,
   generally alternating in further nesting.  The SDF-defined vocabulary
   items used in the hierarchy of such groups are often, but not always,
   called _Quality Names_ or _qualities_. See Section 2.3 for more
   information about naming in SDF.

2.2.  Elements of an SDF Model

   The SDF language uses six predefined Class Name Keywords for modeling
   connected Things, which are illustrated in Figure 2 (limited
   rendition in the plaintext form of this document, please use
   typographic forms for full information).

                                 ,--------.
                                 |sdfThing|------.
                  ,--------------|--------|      | hasThing
                  |              |--------|<-----'
                  |              `--------'
                  |                |   | |
                  |      hasObject |   |  \
                  |                v   |   \
                  |        ,---------. |    \
                  |        |sdfObject| |     \
                  |        |---------| |      \
                  ,--------|---------|---------.
                  |        `---------' |       |
               has|Property     | hasAction    | hasEvent
                  v             v      v       v
               ,-----------.  ,---------.   ,--------.
               |sdfProperty|  |sdfAction|   |sdfEvent|
               |-----------|  |---------|   |--------|
               |-----------|  |---------|   |--------|
               `-----------'  `---------'   `--------'
                  |      hasInput|   |hasOutput    |
                  |          Data|   |Data         |
                  |              v   v             |
                  |            ,-------.           |
                  | isInst     |sdfData|  hasOutp  |
                  `----------->|-------|<----------'
                    anceOf     |-------|  utData
                               `-------'

                 Figure 2: Main Classes Used in SDF Models

   The six main Class Name Keywords are discussed below.

2.2.1.  sdfObject

   sdfObjects, the items listed in an sdfObject definition group, are
   the main "atom" of reusable semantics for model construction.  The
   concept aligns in scope with common definition items from many IoT
   modeling systems, e.g., ZigBee Clusters [ZCL], OMA SpecWorks LwM2M
   Objects [OMA], OCF Resource Types [OCF], and W3C Web of Things Thing
   Descriptions [WoT].

   An sdfObject definition contains a set of sdfProperty, sdfAction, and
   sdfEvent definitions that describe the interaction affordances
   associated with some scope of functionality.

   For the granularity of definition, sdfObject definitions are meant to
   be kept narrow enough in scope to enable broad reuse and
   interoperability.  For example, defining a light bulb using separate
   sdfObject definitions for on/off control, dimming, and color control
   affordances will enable interoperable functionality to be configured
   for diverse product types.  An sdfObject definition for a common on/
   off control may be used to control many different kinds of Things
   that require on/off control.

   The presence of one or both of the optional qualities "minItems" and
   "maxItems" defines the sdfObject as an array, i.e., all the
   affordances defined for the sdfObject exist a number of times,
   indexed by a number constrained to be between minItems and maxItems,
   inclusive, if given.  (Note: Setting "minItems" to zero and leaving
   out "maxItems" puts the minimum constraints on that array.)

2.2.2.  sdfProperty

   sdfProperty is used to model elements of state within Things modeled
   by the enclosing grouping.

   A named definition entry in an sdfProperty may be associated with
   some protocol affordance to enable the application to obtain the
   state variable and, optionally, modify the state variable.
   Additionally, some protocols provide for in-time reporting of state
   changes.  (These three aspects are described by the qualities
   readable, writable, and observable defined for an sdfProperty.)

   Definitions in sdfProperty groups look like the definitions in
   sdfData groups.  However, they actually declare that a Property with
   the given qualities potentially is present in the containing
   sdfObject.

   For definitions in sdfProperty and sdfData, SDF provides qualities
   that can constrain the structure and values of data allowed in the
   interactions modeled by them.  It also provides qualities that
   associate semantics to this data, such as engineering units and unit
   scaling information.

   For the data definition within sdfProperty or sdfData, SDF borrows
   some vocabulary proposed for drafts 4 [JSO4] [JSO4V] and 7 [JSO7]
   [JSO7V] of the json-schema.org "JSON Schema" format (collectively
   called JSO here), enhanced by qualities that are specific to SDF.
   Details about the JSO-inspired vocabulary are in Appendix C.  For
   base SDF, data are constrained to be of simple types (number, string,
   boolean), JSON maps composed of named data, and arrays of these
   types.  Syntax extension points are provided that can be used to
   provide richer types in a future extension of this specification
   (possibly more of which can be borrowed from json-schema.org).

   Note that sdfProperty definitions (and sdfData definitions in
   general) are not intended to constrain the formats of data used for
   communication over network interfaces.  Where needed, data
   definitions for payloads of protocol messages are expected to be part
   of the protocol binding.

2.2.3.  sdfAction

   The sdfAction group contains declarations of Actions, which model
   affordances that, when triggered, have an effect that can go beyond
   just reading, updating, or observing Thing state.  Actions often
   result in some outward physical effect (which, itself, cannot be
   modeled in SDF).  From a programmer's perspective, they might be
   considered to be roughly analogous to method calls.

   Actions may have data parameters; these are each modeled as a single
   item of input data and output data.  Where multiple parameters need
   to be modeled, an "object" type can be used to combine these
   parameters into one; for an example, see Figure 6 in Appendix C.5.

   Actions may be long-running, that is to say that the effects may not
   take place immediately as would be expected for an update to an
   sdfProperty; the effects may play out over time and emit action
   results.  Actions may also not always complete and may result in
   application errors, such as an item blocking the closing of an
   automatic door.

   One idiom for giving an action initiator status and control about the
   ongoing action is to provide a URI for an ephemeral "action resource"
   in the sdfAction output data, allowing the action to deliver
   immediate feedback (including errors that prevent the action from
   starting) and the action initiator to use the action resource for
   further observation or modification of the ongoing action (including
   canceling it).  Base SDF does not provide any tailored support for
   describing such action resources; an extension for modeling links in
   more detail (for instance, [SDFTYPE-LINK]) may be all that is needed
   to fully enable modeling them.

   Actions may have (or lack) the characteristics of idempotence and
   side-effect safety (see Section 9.2 of RFC 9110 [STD97] for more on
   these terms).

   Base SDF only provides data constraint modeling and semantics for the
   input and output data of definitions in sdfAction groups.  Again,
   data definitions for payloads of protocol messages, and detailed
   protocol settings for invoking the action, are expected to be part of
   the protocol binding.

2.2.4.  sdfEvent

   The sdfEvent group contains declarations of Events, which model
   affordances that inform about "happenings" associated with a Thing
   modeled by the enclosing sdfObject; these may result in a signal
   being stored or emitted as a result.

   Note that there is a trivial overlap with sdfProperty state changes,
   which may also be defined as Events but are not generally required to
   be defined as such.  However, Events may exhibit certain ordering,
   consistency, and reliability requirements that are expected to be
   supported in various implementations of sdfEvent that do distinguish
   sdfEvent from sdfProperty.  For instance, while a state change may
   simply be superseded by another state change, some Events are
   "precious" and need to be preserved even if further Events follow.

   Base SDF only provides data constraint modeling and semantics for the
   output data of Event affordances.  Again, data definitions for
   payloads of protocol messages, and detailed protocol settings for
   soliciting the event, are expected to be part of the protocol
   binding.

2.2.5.  sdfData

   Definitions in sdfData groups do not themselves specify affordances.
   These definitions are provided separately from those in sdfProperty
   groups to enable common modeling patterns, data constraints, and
   semantic anchor concepts to be factored out for data items that make
   up sdfProperty items and serve as input and output data for sdfAction
   and sdfEvent items.  The data types defined in sdfData definitions
   only spring to life by being referenced in one of these contexts
   (directly or indirectly via some other sdfData definitions).

   It is a common use case for such a data definition to be shared
   between an sdfProperty item and input or output parameters of an
   sdfAction or output data provided by an sdfEvent. sdfData definitions
   also enable factoring out extended application data types, such as
   mode and machine state enumerations to be reused across multiple
   definitions that have similar basic characteristics and requirements.

2.2.6.  sdfThing

   Back at the top level, the sdfThing group enables definition of
   models for complex devices that will use one or more sdfObject
   definitions.  Like sdfObject, sdfThing groups allow for the inclusion
   of interaction affordances, sdfData, as well as "minItems" and
   "maxItems" qualities.  Therefore, they can be seen as a superset of
   sdfObject groups, additionally allowing for composition.

   As a result, an sdfThing directly or indirectly contains a set of
   sdfProperty, sdfAction, and sdfEvent definitions that describe the
   interaction affordances associated with some scope of functionality.

   A definition in an sdfThing group can refine the metadata of the
   definitions it is composed of: other definitions in sdfThing groups
   or definitions in sdfObject groups.

2.3.  Member Names: Given Names and Quality Names

   SDF documents are JSON maps that mostly employ JSON maps as member
   values, which in turn mostly employ JSON maps as their member values,
   and so on.  This nested structure of JSON maps creates a tree, where
   the edges are the member names (map keys) used in these JSON maps.
   (In certain cases, where member names are not needed, JSON arrays may
   be interspersed in this tree.)

2.3.1.  Given Names and Quality Names

   For any particular JSON map in an SDF document, the set of member
   names that are used is either:

   *  A set of "_Quality Names_", where the entries in the map are
      Qualities.  Quality Names are defined by the present specification
      and its extensions, together with specific semantics to be
      associated with the member value given with a certain Quality
      Name.

   *  A set of "_Given Names_", where the entries in the map are
      separate entities (definitions, declarations, etc.) that each have
      names that are chosen by the SDF document author in order that
      these names can be employed by a user of that model.

   In a path from the root of the tree to any leaf, Quality Names and
   Given Names roughly alternate (with the information block,
   Section 3.1, as a prominent exception).

   The meaning of the JSON map that is the member value associated with
   a Given Name is derived from the Quality Name that was used as the
   member name associated to the parent.  In the CDDL grammar given in
   Appendix A, JSON maps with member names that are Given Names are
   defined using the CDDL generic rule reference named<membervalues>,
   where membervalues is in turn the structure of the member values of
   the JSON map, i.e., the value of the member named by the Given Name.
   As quality-named maps and given-named maps roughly alternate in a
   path down the tree, membervalues is usually a map built from Quality
   Names as keys.

2.3.2.  Hierarchical Names

   From the outside of a specification, Given Names are usually used as
   part of a hierarchical name that looks like a JSON Pointer [RFC6901].
   These hierarchical names are generally rooted in (used as the
   fragment identifier in) an outer namespace that looks like an
   https:// URL (see Section 4).

   As Quality Names and Given Names roughly alternate in a path into the
   model, the JSON Pointer part of the hierarchical name also alternates
   between Quality Names and Given Names.

   Note that the actual Given Names may need to be encoded when
   specified via the JSON Pointer fragment identifier syntax.  There are
   two layers of such encoding: tilde encoding of ~ and / as per
   Section 3 of [RFC6901], as well as percent encoding of the tilde-
   encoded name into a valid URI fragment as per Section 6 of [RFC6901].
   For example, when a model is using the Given Name

      warning/danger alarm

   (with an embedded slash and a space) for an sdfObject, that sdfObject
   may need to be referenced as

      #/sdfObject/warning~1danger%20alarm

   To sidestep potential interoperability problems, it is probably wise
   to avoid characters in Given Names that need such encoding (Quality
   Names are already defined in such a way that they never do).

2.3.3.  Extensibility of Given Names and Quality Names

   In SDF, both Quality Names and Given Names are _extension points_.
   This is more obvious for Quality Names.  Extending SDF is mostly done
   by defining additional qualities.  To enable non-conflicting third
   party extensions to SDF, qualified names (names with an embedded
   colon) can be used as Quality Names.

   A nonqualified Quality Name is composed of ASCII letters, digits, and
   $ signs, starting with a lowercase letter or a $ sign (i.e., using a
   pattern of "[a-z$][A-Za-z$0-9]*").  Names with $ signs are intended
   to be used for functions separate from most other names; for
   instance, $comment is used for the comment quality in this
   specification (the presence or absence of a $comment quality does not
   change the meaning of the SDF model).  Names that are composed of
   multiple English words can use the "lowerCamelCase" convention
   [CamelCase] for indicating the word boundaries; no other use is
   intended for upper case letters in Quality Names.

   A qualified Quality Name is composed of a Quality Name Prefix, a :
   (colon) character, and a nonqualified Quality Name.  Quality Name
   Prefixes are registered in the "Quality Name Prefixes" registry in
   the "Semantic Definition Format (SDF)" registry group
   (Section 7.5.2).  They are composed of lowercase ASCII letters and
   digits, starting with a lowercase ASCII letter (i.e., using a pattern
   of "[a-z][a-z0-9]*").

   Given Names are not restricted by the formal SDF syntax.  To enable
   non-surprising name translations in tools, combinations of ASCII
   alphanumeric characters and - (ASCII hyphen/minus) are preferred,
   typically employing kebab-case for names constructed out of multiple
   words [KebabCase].  ASCII hyphen/minus can then unambiguously be
   translated to an ASCII _ underscore character and back depending on
   the programming environment.  Some styles also allow a dot (".") in
   Given Names.  Given Names are often sufficiently self-explanatory
   that they can be used in place of the label quality if that is not
   given.  In turn, if a Given Name turns out too complicated, a more
   elaborate label can be given and the Given Name kept simple.  As
   Given Names are "programmers' names", base SDF does not address
   internationalization of Given Names.  (More likely qualities to
   receive localizable equivalents by exercising the Quality Name
   extension point are label and description).

   Further, to enable Given Names to have a more powerful role in
   building global hierarchical names, an extension is foreseen that
   makes use of qualified names for Given Names.  So, until that
   extension is defined, Given Names with one or more embedded colons
   are reserved and MUST NOT be used in an SDF document.

   All names in SDF are case-sensitive.

3.  SDF Structure

   SDF definitions are contained in SDF documents together with data
   about the SDF document itself (information block).  Definitions and
   declarations from additional SDF documents can be referenced;
   together with the definitions and declarations in the referencing SDF
   document, they build the SDF model expressed by that SDF document.

   Each SDF document is represented as a single JSON map.  This map can
   be thought of as having three blocks: the information block, the
   namespaces block, and the definitions block.  These blocks contain
   zero or more JSON name/value pairs, the names of which are Quality
   Names and the values of which mostly are (nested) maps (the exception
   defined in base SDF is the defaultNamespace quality, the value of
   which is a text string).  An empty nested map of this kind is
   equivalent to not having the quality included at all.

3.1.  Information Block

   The information block contains generic metadata for the SDF document
   itself and all included definitions.  To enable tool integration, the
   information block is optional in the grammar of SDF; most processes
   for working with SDF documents will have policies that only SDF
   documents with an info block can be processed.  It is therefore
   RECOMMENDED that SDF validator tools emit a warning when no
   information block is found.

   The keyword (map key) that defines an information block is "info".
   The keyword's value is a nested JSON map with a set of entries that
   represent qualities that apply to the included definitions.

   Qualities of this map are shown in Table 1.  None of these qualities
   are required or have default values that are assumed if the quality
   is absent.

       +=============+==========+=================================+
       | Quality     | Type     | Description                     |
       +=============+==========+=================================+
       | title       | string   | A short summary to be displayed |
       |             |          | in search results, etc.         |
       +-------------+----------+---------------------------------+
       | description | string   | Long-form text description (no  |
       |             |          | constraints)                    |
       +-------------+----------+---------------------------------+
       | version     | string   | The incremental version of the  |
       |             |          | definition                      |
       +-------------+----------+---------------------------------+
       | modified    | string   | Time of the latest modification |
       +-------------+----------+---------------------------------+
       | copyright   | string   | Link to text or embedded text   |
       |             |          | containing a copyright notice   |
       +-------------+----------+---------------------------------+
       | license     | string   | Link to text or embedded text   |
       |             |          | containing license terms        |
       +-------------+----------+---------------------------------+
       | features    | array of | List of extension features used |
       |             | strings  |                                 |
       +-------------+----------+---------------------------------+
       | $comment    | string   | Source code comments only, no   |
       |             |          | semantics                       |
       +-------------+----------+---------------------------------+

               Table 1: Qualities of the Information Block

   The version quality is used to indicate version information about the
   set of definitions in the SDF document.  The version is RECOMMENDED
   to be lexicographically increasing over the life of a model; a newer
   model always has a version string that string-compares higher than
   all previous versions.  This is easily achieved by following the
   convention to start the version with a date-time as defined in
   [RFC3339] or, if new versions are generated less frequently than once
   a day, just the full-date (i.e., YYYY-MM-DD); in many cases, that
   will be all that is needed (see Figure 1 for an example).  This
   specification does not give a strict definition for the format of the
   version string, but each system or organization using the version
   string should define internal structure and semantics to the level
   needed for their use.  If no further details are provided, a date-
   time or full-date in this field can be assumed to indicate the latest
   update time of the definitions in the SDF document.

   The modified quality can be used with a value using date-time as
   defined in [RFC3339] (with Z for time-zone) or full-date format to
   express time of the latest revision of the definitions.

   The license string is preferably either a URI that points to a web
   page with an unambiguous definition of the license or an [SPDX]
   license identifier.  (As an example, for models to be handled by the
   One Data Model liaison group, this license identifier will typically
   be "BSD-3-Clause".)

   The features quality can be used to list names of critical (i.e.,
   cannot be safely ignored) SDF extension features that need to be
   understood for the definitions to be properly processed.  Extension
   feature names will be specified in extension documents.  They can
   either be registered (see Section 7.5.4 for specifics, which make
   sure that a registered feature name does not contain a colon) or be a
   URI (which always contain a colon).  Note that SDF processors are not
   expected to, and normally SHOULD NOT, dereference URIs used as
   feature names; any representation retrievable under such a URI could
   be useful to humans, though.  (See [DEREF-ID-PATTERN] for a more
   extensive discussion of dereferenceable identifiers).

3.2.  Namespaces Block

   The namespaces block contains the namespace map and the
   defaultNamespace setting; none of these qualities are required or
   have default values that are assumed if the quality is absent.

   The namespace map is a map from short names for URIs to the namespace
   URIs themselves.

   The defaultNamespace setting selects one of the entries in the
   namespace map by giving its short name.  The associated URI (value of
   this entry) becomes the default namespace for the SDF document.

     +==================+========+===================================+
     | Quality          | Type   | Description                       |
     +==================+========+===================================+
     | namespace        | map    | Defines short names mapped to     |
     |                  |        | namespace URIs, to be used as     |
     |                  |        | identifier prefixes               |
     +------------------+--------+-----------------------------------+
     | defaultNamespace | string | Identifies one of the prefixes in |
     |                  |        | the namespace map to be used as a |
     |                  |        | default in resolving identifiers  |
     +------------------+--------+-----------------------------------+

                         Table 2: Namespaces Block

   The following example declares a set of namespaces and defines cap as
   the default namespace.  By convention, the values in the namespace
   map contain full URIs without a fragment identifier and the fragment
   identifier is then added, if needed, where the namespace entry is
   used.

   "namespace": {
     "cap": "https://example.com/capability/cap",
     "zcl": "https://zcl.example.com/sdf"
   },
   "defaultNamespace": "cap"

   Multiple SDF documents can contribute to the same namespace by using
   the same namespace URI for the default namespace across the
   documents.

   If no defaultNamespace setting is given, the SDF document does not
   contribute to a global namespace (all definitions remain local to the
   model and are not accessible for re-use by other models).  As the
   defaultNamespace is set by supplying a namespace short name, its
   presence requires a namespace map that contains a mapping for that
   namespace short name.

   If no namespace map is given, no short names for namespace URIs are
   set up and no defaultNamespace can be given.

3.3.  Definitions Block

   The Definitions block contains one or more groups, each identified by
   a Class Name Keyword such as sdfObject or sdfProperty.  There can
   only be one group per keyword at this level; putting all the
   individual definitions in the group under that keyword is just a
   shortcut for identifying the class name keyword that applies to each
   of them without repeating it for each definition.

   The value of each group is a JSON map, the keys of which serve for
   naming the individual definitions in this group, and the
   corresponding values provide a set of qualities (name-value pairs)
   for the individual definition.  (In short, these map entries are also
   termed "named sets of qualities".)

   Each group may contain zero or more definitions.  Each identifier
   defined creates a new type and term in the target namespace.
   Declarations have a scope of the definition block they are directly
   contained in.

   In turn, a definition may contain other definitions.  Each definition
   is a named set of qualities, i.e., it consists of the newly defined
   identifier and a set of key-value pairs that represent the defined
   qualities and contained definitions.

   An example for an sdfObject definition is given in Figure 3:

   "sdfObject": {
     "foo": {
       "sdfProperty": {
         "bar": {
           "type": "boolean"
         }
       }
     }
   }

                   Figure 3: Example sdfObject Definition

   This example defines an sdfObject "foo" that is defined in the
   default namespace (full address: #/sdfObject/foo), containing a
   Property that can be addressed as #/sdfObject/foo/sdfProperty/bar,
   with data of type boolean.

   Often, definitions are also declarations.  The definition of the
   entry "bar" in the Property "foo" means that data corresponding to
   the "foo" Property in a Property interaction offered by Thing can
   have zero or one components modeled by "bar".  Entries within
   sdfProperty, sdfAction, and sdfEvent that are in turn within
   sdfObject or sdfThing entries, are also declarations; entries within
   sdfData are not.  Similarly, sdfObject or sdfThing entries within an
   sdfThing definition specify that the interactions offered by a Thing
   modeled by this sdfThing include the interactions modeled by the
   nested sdfObject or sdfThing.

3.4.  Top-Level Affordances and sdfData

   Besides their placement within an sdfObject or sdfThing, affordances
   (i.e., sdfProperty, sdfAction, and sdfEvent) as well as sdfData can
   also be placed at the top level of an SDF document.  Since they are
   not associated with an sdfObject or sdfThing, these kinds of
   definitions are intended to be reused via the sdfRef mechanism (see
   Section 4.4).

4.  Names and Namespaces

   SDF documents may contribute to a global namespace and may reference
   elements from that global namespace.  (An SDF document that does not
   set a defaultNamespace does not contribute to a global namespace.)

4.1.  Structure

   Global names look exactly like https:// URIs with attached fragment
   identifiers.

   There is no intention to require that these URIs can be dereferenced.
   (However, as future extensions of SDF might find a use for
   dereferencing global names, the URI should be chosen in such a way
   that this may become possible in the future.  See also
   [DEREF-ID-PATTERN] for a discussion of dereferenceable identifiers.)

   The absolute-URI of a global name should be a URI as per Section 3 of
   RFC 3986 [STD66] with a scheme of "https" and a path (hier-part in
   [STD66]).  For base SDF, the query part should not be used (it might
   be used in extensions).

   The fragment identifier is constructed as per Section 6 of [RFC6901].

4.2.  Contributing Global Names

   The fragment identifier part of a global name defined in an SDF
   document is constructed from a JSON Pointer that selects the element
   defined for this name in the SDF document.  The absolute-URI part is
   a copy of the default namespace.

   As a result, the default namespace is always the target namespace for
   a name for which a definition is contributed.  In order to emphasize
   that name definitions are contributed to the default namespace, this
   namespace is also termed the "target namespace" of the SDF document.

   For instance, in Figure 1, definitions for the following global names
   are contributed:

   *  https://example.com/capability/cap#/sdfObject/Switch

   *  https://example.com/capability/cap#/sdfObject/Switch/sdfProperty/
      value

   *  https://example.com/capability/cap#/sdfObject/Switch/sdfAction/on

   *  https://example.com/capability/cap#/sdfObject/Switch/sdfAction/off

   *  https://example.com/capability/cap#/sdfObject/Switch/sdfAction/
      toggle

   Note the #, which separates the absolute-URI part (Section 4.3 of RFC
   3986 [STD66]) from the fragment identifier part (including the #, a
   JSON Pointer as in Section 6 of [RFC6901]).

4.3.  Referencing Global Names

   A name reference takes the form of the production curie in Section 3
   of [W3C.NOTE-curie-20101216], but limiting the IRIs involved in that
   grammar to URIs as per [STD66] and the prefixes to ASCII characters
   [STD80].  (Note that this definition does not make use of the
   production safe-curie in [W3C.NOTE-curie-20101216].)

   A name that is contributed by the current SDF document can be
   referenced by a Same-Document Reference as per Section 4.4 of RFC
   3986 [STD66].  As there is little point in referencing the entire SDF
   document, this will be a # followed by a JSON Pointer.  This is the
   only kind of name reference to itself that is possible in an SDF
   document that does not set a default namespace.

   Name references that point outside the current SDF document need to
   contain CURIE prefixes.  These then reference namespace declarations
   in the namespaces block.

   For example, if a namespace prefix is defined:

   "namespace": {
     "foo": "https://example.com/"
   }

   then this reference to that namespace:

   "sdfRef": "foo:#/sdfData/temperatureData"

   references the global name:

   "https://example.com/#/sdfData/temperatureData"

   Note that there is no way to provide a URI scheme name in a CURIE, so
   all references to outside of the document need to go through the
   namespace map.

   Name references occur only in specific elements of the syntax of SDF:

   *  copying elements via sdfRef values

   *  pointing to elements via sdfRequired value elements

4.4.  sdfRef

   In a JSON map establishing a definition, the keyword sdfRef is used
   to copy the qualities and enclosed definitions of the referenced
   definition, indicated by the included name reference, into the newly
   formed definition.  (This can be compared to the processing of the
   $ref keyword in [JSO7].)  The referenced definition should be such
   that, after copying and applying the additional qualities in the
   referencing definition, the newly built definition is also valid SDF
   (e.g., the copied qualities and definitions are valid in the context
   of the new definition).

   For example, this reference:

   "temperatureProperty": {
     "sdfRef": "#/sdfData/temperatureData"
   }

   creates a new definition "temperatureProperty" that contains all of
   the qualities defined in the definition at /sdfData/temperatureData.

   The sdfRef member need not be the only member of a map.  Additional
   members may be present with the intention of overriding parts of the
   referenced map or adding new qualities or definitions.

   When processing sdfRef, if the target definition contains also sdfRef
   (i.e., is based on yet another definition), that MUST be processed as
   well.

   More formally, for a JSON map that contains an sdfRef member, the
   semantics are defined to be as if the following steps were performed:

   1.  The JSON map that contains the sdfRef member is copied into a
       variable named "patch".

   2.  The sdfRef member of the copy in "patch" is removed.

   3.  The JSON Pointer that is the value of the sdfRef member is
       dereferenced and the result is copied into a variable named
       "original".

   4.  The JSON Merge Patch algorithm [RFC7396] is applied to patch the
       contents of "original" with the contents of "patch".

   5.  The result of the Merge Patch is used in place of the value of
       the original JSON map.

   Note that the formal syntaxes given in Appendices A and B generally
   describe the _result_ of applying a merge-patch.  The notations are
   not powerful enough to describe, for instance, how the merge-patch
   algorithm causes null values within the sdfRef to remove members of
   JSON maps from the referenced target.  Nonetheless, the syntaxes also
   give the syntax of the sdfRef itself, which vanishes during the
   resolution; therefore, in many cases, even merge-patch inputs will
   validate with these formal syntaxes.

   Given the example (Figure 1) and the following definition:

   {
     "info": {
       "title": "Example light switch using sdfRef"
     },
     "namespace": {
       "cap": "https://example.com/capability/cap"
     },
     "defaultNamespace": "cap",
     "sdfObject": {
       "BasicSwitch": {
         "sdfRef": "cap:#/sdfObject/Switch",
         "sdfAction": {
           "toggle": null
         }
       }
     }
   }

   The resulting definition of the "BasicSwitch" sdfObject would be
   identical to the definition of the "Switch" sdfObject, except it
   would not contain the "toggle" Action.

   {
     "info": {
       "title": "Example light switch using sdfRef"
     },
     "namespace": {
       "cap": "https://example.com/capability/cap"
     },
     "defaultNamespace": "cap",
     "sdfObject": {
       "BasicSwitch": {
         "sdfProperty": {
           "value": {
             "description":
   "The state of the switch; false for off and true for on.",
             "type": "boolean"
           }
         },
         "sdfAction": {
           "on": {
             "description":
   "Turn the switch on; equivalent to setting value to true."
           },
           "off": {
             "description":
   "Turn the switch off; equivalent to setting value to false."
           }
         }
       }
     }
   }

4.4.1.  Resolved Models

   A model where all sdfRef references are processed as described in
   Section 4.4 is called a resolved model.

   For example, given the following sdfData definitions:

   "sdfData": {
     "Coordinate" : {
       "type": "number", "unit": "m"
     },
     "X-Coordinate" : {
       "sdfRef" : "#/sdfData/Coordinate",
       "description":
   "Distance from the base of the Thing along the X axis."
     },
     "Non-neg-X-Coordinate" : {
       "sdfRef": "#/sdfData/X-Coordinate",
       "minimum": 0
     }
   }

   the definitions would look as follows after being resolved:

   "sdfData": {
     "Coordinate" : {
       "type": "number", "unit": "m"
     },
     "X-Coordinate" : {
       "description":
   "Distance from the base of the Thing along the X axis.",
       "type": "number", "unit": "m"
     },
     "Non-neg-X-Coordinate" : {
       "description":
   "Distance from the base of the Thing along the X axis.",
       "minimum": 0, "type": "number", "unit": "m"
     }
   }

4.5.  sdfRequired

   The keyword sdfRequired is provided to apply a constraint that
   defines for which declarations the corresponding data are mandatory
   in a grouping (sdfThing or sdfObject) modeled by the current
   definition.

   The value of sdfRequired is an array of references, each indicating
   one or more declarations that are mandatory to be represented.

   References in this array can be SDF names (JSON Pointers) or one of
   two abbreviated reference formats:

   *  A text string with a "referenceable-name", namely an affordance
      name or a grouping name:

      -  All affordance declarations that are directly in the same
         grouping (i.e., not nested further in another grouping) and
         that carry this name are declared to be mandatory to be
         represented.  Note that there can be multiple such affordance
         declarations, one per affordance type.

      -  The same applies to groupings made mandatory within groupings
         containing them.

   *  The Boolean value true.  The affordance or grouping itself that
      carries the sdfRequired keyword is declared to be mandatory to be
      represented.

   Note that referenceable-names are not subject to the encoding JSON
   Pointers require as discussed in Section 2.3.2.  To ensure that
   referenceable-names are reliably distinguished from JSON Pointers,
   they are defined such that they cannot contain ":" or "#" characters
   (see rule referenceable-name in Appendix A).  (If these characters
   are indeed contained in a Given Name, a JSON Pointer needs to be
   formed instead in order to reference it in "sdfRequired", potentially
   requiring further path elements as well as JSON Pointer encoding.
   The need for this is best avoided by choosing Given Names without
   these characters.)

   The example in Figure 4 shows two required elements in the sdfObject
   definition for "temperatureWithAlarm", the sdfProperty
   "currentTemperature", and the sdfEvent "overTemperatureEvent".  The
   example also shows the use of JSON Pointers with "sdfRef" to use a
   pre-existing definition for the sdfProperty "currentTemperature" and
   for the sdfOutputData produced by the sdfEvent
   "overTemperatureEvent".

   "sdfObject": {
     "temperatureWithAlarm": {
       "sdfRequired": [
   "#/sdfObject/temperatureWithAlarm/sdfProperty/currentTemperature",
   "#/sdfObject/temperatureWithAlarm/sdfEvent/overTemperatureEvent"
       ],
       "sdfData":{
          "temperatureData": {
           "type": "number"
         }
       },
       "sdfProperty": {
         "currentTemperature": {
   "sdfRef": "#/sdfObject/temperatureWithAlarm/sdfData/temperatureData",
         "writable": false
         }
       },
       "sdfEvent": {
         "overTemperatureEvent": {
          "sdfOutputData": {
   "sdfRef": "#/sdfObject/temperatureWithAlarm/sdfData/temperatureData"
           }
         }
       }
     }
   }

                        Figure 4: Using sdfRequired

   In Figure 4, the same sdfRequired can also be represented in short
   form:

       "sdfRequired": ["currentTemperature", "overTemperatureEvent"]

   Or, for instance, "overTemperatureEvent" could carry:

         "overTemperatureEvent": {
           "sdfRequired": [true],
           "...": "..."
         }

4.6.  Common Qualities

   Definitions in SDF share a number of qualities that provide metadata
   for them.  These are listed in Table 3.  None of these qualities are
   required or have default values that are assumed if the quality is
   absent.  If a short textual description is required for an
   application and no label is given in the SDF model, applications
   could use the last part (the last reference-token, Section 3 of
   [RFC6901]) of the JSON Pointer to the definition in its place.

       +=============+==============+=============================+
       | Quality     | Type         | Description                 |
       +=============+==============+=============================+
       | description | string       | long text (no constraints)  |
       +-------------+--------------+-----------------------------+
       | label       | string       | short text (no constraints) |
       +-------------+--------------+-----------------------------+
       | $comment    | string       | source code comments only,  |
       |             |              | no semantics                |
       +-------------+--------------+-----------------------------+
       | sdfRef      | sdf-pointer  | (see Section 4.4)           |
       +-------------+--------------+-----------------------------+
       | sdfRequired | pointer-list | (see Section 4.5, used in   |
       |             |              | affordances or groupings)   |
       +-------------+--------------+-----------------------------+

                        Table 3: Common Qualities

4.7.  Data Qualities

   Data qualities are used in sdfData and sdfProperty definitions, which
   are named sets of data qualities (abbreviated as named-sdq).

   These qualities include the common qualities, JSO-inspired qualities
   (see below), and data qualities defined specifically for the present
   specification; the latter are shown in Table 4.

   Appendix C lists data qualities inspired by the various proposals at
   json-schema.org; the intention is that these (information model-
   level) qualities are compatible with the (data model) semantics from
   the versions of the json-schema.org proposal they were imported from.

     +===============+================+====================+=========+
     | Quality       | Type           | Description        | Default |
     +===============+================+====================+=========+
     | (common)      |                | Section 4.6        |         |
     +---------------+----------------+--------------------+---------+
     | unit          | string         | unit name (note 1) | N/A     |
     +---------------+----------------+--------------------+---------+
     | nullable      | boolean        | indicates a null   | true    |
     |               |                | value is available |         |
     |               |                | for this type      |         |
     +---------------+----------------+--------------------+---------+
     | contentFormat | string         | content type (IANA | N/A     |
     |               |                | media type string  |         |
     |               |                | plus parameters),  |         |
     |               |                | encoding (note 2)  |         |
     +---------------+----------------+--------------------+---------+
     | sdfType       | string         | sdfType            | N/A     |
     |               | (Section       | enumeration        |         |
     |               | 4.7.1)         | (extensible)       |         |
     +---------------+----------------+--------------------+---------+
     | sdfChoice     | named set of   | named alternatives | N/A     |
     |               | data qualities |                    |         |
     |               | (Section       |                    |         |
     |               | 4.7.2)         |                    |         |
     +---------------+----------------+--------------------+---------+
     | enum          | array of       | abbreviation for   | N/A     |
     |               | strings        | string-valued      |         |
     |               |                | named alternatives |         |
     +---------------+----------------+--------------------+---------+

         Table 4: SDF-Defined Qualities of sdfData and sdfProperty

   1.  The unit name SHOULD be as per the "SenML Units" registry or the
       "Secondary Units" registry in [IANA.senml] as specified by
       Sections 4.5.2 and 12.1 of [RFC8428] and Section 3 of [RFC8798],
       respectively.

       Exceptionally, if a registration in these registries cannot be
       obtained or would be inappropriate, the unit name can also be a
       URI that is pointing to a definition of the unit.  Note that SDF
       processors are not expected to, and normally SHOULD NOT,
       dereference these URIs; the definition pointed to may be useful
       to humans, though.  (See [DEREF-ID-PATTERN] for a more extensive
       discussion of dereferenceable identifiers).

       A URI unit name is distinguished from a registered unit name by
       the presence of a colon; therefore, any registered unit names
       that contain a colon (at the time of writing, none) cannot be
       directly used in SDF.

       For use by translators into ecosystems that require URIs for unit
       names, the URN sub-namespace "urn:ietf:params:unit" is provided
       (Section 7.3).  URNs from this sub-namespace MUST NOT be used in
       a unit quality in favor of simply notating the unit name (such as
       kg instead of urn:ietf:params:unit:kg) except where the unit name
       contains a colon and can therefore not be directly used in SDF.

   2.  The contentFormat quality follows the Content-Format-Spec as
       defined in Section 6 of [RFC9193], allowing for expressing both
       numeric and string based Content-Formats.

4.7.1.  sdfType

   SDF defines a number of basic types beyond those provided by JSON or
   JSO.  These types are identified by the sdfType quality, which is a
   text string from a set of type names defined by the "sdfType values"
   registry in the "Semantic Definition Format (SDF)" registry group
   (Section 7.5.3).  The sdfType name is composed of lowercase ASCII
   letters, digits, and - (ASCII hyphen/minus) characters, starting with
   a lowercase ASCII letter (i.e., using a pattern of "[a-z][-a-z0-9]*")
   and typically employing kebab-case for names constructed out of
   multiple words [KebabCase].

   To aid interworking with JSO implementations, it is RECOMMENDED that
   sdfType is always used in conjunction with the type quality inherited
   from [JSO7V] in such a way as to yield a common representation of the
   type's values in JSON.

   Values for sdfType that are defined in this specification are shown
   in Table 5.  This table also gives a description of the semantics of
   the sdfType, the conventional value for type to be used with the
   sdfType value, and a conventional JSON representation for values of
   the type.  The type and the JSON representation are chosen to be
   consistent with each other; this MUST be true for additionally
   registered sdfType values as well.

   +=============+=============+========+================+============+
   | Name        | Description | type   | JSON           | Reference  |
   |             |             |        | Representation |            |
   +=============+=============+========+================+============+
   | byte-string | A sequence  | string | base64url      | Section    |
   |             | of zero or  |        | without        | 3.4.5.2 of |
   |             | more bytes  |        | padding        | RFC 8949   |
   |             |             |        |                | [STD94]    |
   +-------------+-------------+--------+----------------+------------+
   | unix-time   | A point in  | number | POSIX time     | Section    |
   |             | civil time  |        |                | 3.4.2 of   |
   |             | (note 1)    |        |                | RFC 8949   |
   |             |             |        |                | [STD94]    |
   +-------------+-------------+--------+----------------+------------+

       Table 5: Values Defined in Base SDF for the sdfType Quality

   (1) Note that the definition of unix-time does not imply the
   capability to represent points in time that fall on leap seconds.
   More date/time-related sdfTypes are likely to be added in the sdfType
   value registry.

4.7.2.  sdfChoice

   Data can be a choice of named alternatives called sdfChoice.  Each
   alternative is identified by a name (string, key in the outer JSON
   map used to represent the overall choice) and a set of dataqualities
   (each in an inner JSON map, the value used to represent the
   individual alternative in the outer JSON map).  Dataqualities that
   are specified at the same level as the sdfChoice apply to all choices
   in the sdfChoice except those specific choices where the dataquality
   is overridden at the choice level.

   sdfChoice merges the functions of two constructs found in [JSO7V]:

   *  enum

      What could be expressed as:

      "enum": ["foo", "bar", "baz"]

      in JSO, is often best represented as:

      "sdfChoice": {
        "foo": { "description": "This is a foonly"},
        "bar": { "description":
                 "As defined in the second world congress"},
        "baz": { "description": "From bigzee foobaz"}
      }

      This allows the placement of other dataqualities such as
      description in the example.

      If an enum needs to use a data type different from the text
      string, what would, for instance, have been:

      "type": "number",
      "enum": [1, 2, 3]

      in JSO, is represented as:

      "type": "number",
      "sdfChoice": {
        "a-better-name-for-alternative-1": { "const": 1 },
        "alternative-2": { "const": 2 },
        "the-third-alternative": { "const": 3 }
      }

      where the string names obviously would be chosen in a way that is
      descriptive for what these numbers actually stand for; sdfChoice
      also makes it easy to add number ranges into the mix.

      (Note that const can also be used for strings as in the previous
      example, for instance, if the actual string value is indeed a
      crucial element for the data model.)

   *  anyOf

      JSO provides a type union called anyOf, which provides a choice
      between anonymous alternatives.

      What could have been in JSO:

      "anyOf": [
        {"type": "array", "minItems": 3, "maxItems": "3",
         "items": {"$ref": "#/sdfData/rgbVal"}},
        {"type": "array", "minItems": 4, "maxItems": "4",
         "items": {"$ref": "#/sdfData/cmykVal"}}
      ]

      can be more descriptively notated in SDF as:

      "sdfChoice": {
        "rgb": {"type": "array", "minItems": 3, "maxItems": "3",
                "items": {"sdfRef": "#/sdfData/rgbVal"}},
        "cmyk": {"type": "array", "minItems": 4, "maxItems": "4",
                 "items": {"sdfRef": "#/sdfData/cmykVal"}}
      }

   Note that there is no need in SDF for the type intersection construct
   allOf or the peculiar type-xor construct oneOf found in [JSO7V].

   As a simplification for users of SDF models who are accustomed to the
   JSO enum keyword, this is retained, but limited to a choice of text
   string values, such that:

   "enum": ["foo", "bar", "baz"]

   is syntactic sugar for:

   "sdfChoice": {
     "foo": { "const": "foo"},
     "bar": { "const": "bar"},
     "baz": { "const": "baz"}
   }

   In a single definition, the keyword enum cannot be used at the same
   time as the keyword sdfChoice, as the former is just syntactic sugar
   for the latter.

5.  Keywords for Definition Groups

   The following SDF keywords are used to create definition groups in
   the target namespace.  All these definitions share some common
   qualities as discussed in Section 4.6.

5.1.  sdfObject

   The sdfObject keyword denotes a group of zero or more sdfObject
   definitions. sdfObject definitions may contain or include definitions
   of named Properties, Actions, and Events declared for the sdfObject,
   as well as named data types (sdfData group) to be used in this or
   other sdfObjects.

   The qualities of an sdfObject include the common qualities;
   additional qualities are shown in Table 6.  None of these qualities
   are required or have default values that are assumed if the quality
   is absent.

       +=============+===========+================================+
       | Quality     | Type      | Description                    |
       +=============+===========+================================+
       | (common)    |           | Section 4.6                    |
       +-------------+-----------+--------------------------------+
       | sdfProperty | property  | zero or more named property    |
       |             |           | definitions for this sdfObject |
       +-------------+-----------+--------------------------------+
       | sdfAction   | action    | zero or more named action      |
       |             |           | definitions for this sdfObject |
       +-------------+-----------+--------------------------------+
       | sdfEvent    | event     | zero or more named event       |
       |             |           | definitions for this sdfObject |
       +-------------+-----------+--------------------------------+
       | sdfData     | named-sdq | zero or more named data type   |
       |             |           | definitions that might be used |
       |             |           | in the above                   |
       +-------------+-----------+--------------------------------+
       | minItems    | number    | (array) minimum number of      |
       |             |           | multiplied affordances in      |
       |             |           | array                          |
       +-------------+-----------+--------------------------------+
       | maxItems    | number    | (array) maximum number of      |
       |             |           | multiplied affordances in      |
       |             |           | array                          |
       +-------------+-----------+--------------------------------+

                     Table 6: Qualities of sdfObject

5.2.  sdfProperty

   The sdfProperty keyword denotes a group of zero or more Property
   definitions.

   Properties are used to model elements of state.

   The qualities of a Property definition include the data qualities
   (and thus the common qualities); see Section 4.7.  Additional
   qualities are shown in Table 7.

    +============+=========+===============================+=========+
    | Quality    | Type    | Description                   | Default |
    +============+=========+===============================+=========+
    | (data)     |         | Section 4.7                   |         |
    +------------+---------+-------------------------------+---------+
    | readable   | boolean | Reads are allowed             | true    |
    +------------+---------+-------------------------------+---------+
    | writable   | boolean | Writes are allowed            | true    |
    +------------+---------+-------------------------------+---------+
    | observable | boolean | Flag to indicate asynchronous | true    |
    |            |         | notification is available     |         |
    +------------+---------+-------------------------------+---------+

                    Table 7: Qualities of sdfProperty

5.3.  sdfAction

   The sdfAction keyword denotes a group of zero or more Action
   definitions.

   Actions are used to model commands and methods that are invoked.
   Actions may have parameter data that is supplied upon invocation and
   output data that is provided as a direct result of the invocation of
   the action (note that "action objects" may also be created to furnish
   ongoing information during a long-running action; these would be
   pointed to by the output data).

   The qualities of an Action definition include the common qualities.
   Additional qualities are shown in Table 8.  None of these qualities
   are required or have default values that are assumed if the quality
   is absent.

        +===============+===========+============================+
        | Quality       | Type      | Description                |
        +===============+===========+============================+
        | (common)      |           | Section 4.6                |
        +---------------+-----------+----------------------------+
        | sdfInputData  | map       | data qualities of the      |
        |               |           | input data for an Action   |
        +---------------+-----------+----------------------------+
        | sdfOutputData | map       | data qualities of the      |
        |               |           | output data for an Action  |
        +---------------+-----------+----------------------------+
        | sdfData       | named-sdq | zero or more named data    |
        |               |           | type definitions that      |
        |               |           | might be used in the above |
        +---------------+-----------+----------------------------+

                     Table 8: Qualities of sdfAction

   sdfInputData defines the input data of the action.  sdfOutputData
   defines the output data of the action.  As discussed in
   Section 2.2.3, a set of data qualities with type "object" can be used
   to substructure either data item, with optionality indicated by the
   data quality required.

5.4.  sdfEvent

   The sdfEvent keyword denotes zero or more Event definitions.

   Events are used to model asynchronous occurrences that may be
   communicated proactively.  Events have data elements that are
   communicated upon the occurrence of the event.

   The qualities of sdfEvent include the common qualities.  Additional
   qualities are shown in Table 9.  None of these qualities are required
   or have default values that are assumed if the quality is absent.

        +===============+===========+============================+
        | Quality       | Type      | Description                |
        +===============+===========+============================+
        | (common)      |           | Section 4.6                |
        +---------------+-----------+----------------------------+
        | sdfOutputData | map       | data qualities of the      |
        |               |           | output data for an Event   |
        +---------------+-----------+----------------------------+
        | sdfData       | named-sdq | zero or more named data    |
        |               |           | type definitions that      |
        |               |           | might be used in the above |
        +---------------+-----------+----------------------------+

                      Table 9: Qualities of sdfEvent

   sdfOutputData defines the output data of the action.  As discussed in
   Section 2.2.4, a set of data qualities with type "object" can be used
   to substructure the output data item, with optionality indicated by
   the data quality required.

5.5.  sdfData

   The sdfData keyword denotes a group of zero or more named data type
   definitions (named-sdq).

   An sdfData definition provides a reusable semantic identifier for a
   type of data item and describes the constraints on the defined type.
   sdfData is not itself a declaration, so it does not cause any of
   these data items to be included in an affordance definition.

   The qualities of sdfData include the data qualities (and thus the
   common qualities); see Section 4.7.

6.  High-Level Composition

   The requirements for high-level composition include the following:

   *  The ability to represent products, standardized product types, and
      modular products while maintaining the atomicity of sdfObjects.

   *  The ability to compose a reusable definition block from
      sdfObjects.  Example: a single plug unit of an outlet strip with
      sdfObjects for on/off control, energy monitor, and optional
      dimmer, while retaining the atomicity of the individual
      sdfObjects.

   *  The ability to compose sdfObjects and other definition blocks into
      a higher level sdfThing that represents a product, while retaining
      the atomicity of sdfObjects.

   *  The ability to enrich and refine a base definition to have
      product-specific qualities and quality values, such as unit,
      range, and scale settings.

   *  The ability to reference items in one part of a complex definition
      from another part of the same definition.  Example: summarizing
      the energy readings from all plugs in an outlet strip.

6.1.  Paths in the Model Namespaces

   The model namespace is organized according to terms that are defined
   in the SDF documents that contribute to the namespace.  For example,
   definitions that originate from an organization or vendor are
   expected to be in a namespace that is specific to that organization
   or vendor.

   The structure of a path in a namespace is defined by the JSON
   Pointers to the definitions in the SDF documents in that namespace.
   For example, if there is an SDF document defining an sdfObject
   "Switch" with an action "on", then the reference to the action would
   be "ns:#/sdfObject/Switch/sdfAction/on", where ns is the namespace
   prefix (short name for the namespace).

6.2.  Modular Composition

   Modular composition of definitions enables an existing definition
   (which could be in the same or another SDF document) to become part
   of a new definition by including a reference to the existing
   definition within the model namespace.

6.2.1.  Use of the "sdfRef" Keyword to Reuse a Definition

   An existing definition may be used as a template for a new
   definition, that is, a new definition is created in the target
   namespace that uses the defined qualities of some existing
   definition.  This pattern uses the keyword sdfRef as a quality of a
   new definition with a value consisting of a reference to the existing
   definition that is to be used as a template.

   In the definition that uses sdfRef, new qualities may be added and
   existing qualities from the referenced definition may be overridden.
   (Note that JSON maps do not have a defined order, so the SDF
   processor may see these overrides before seeing the sdfRef.)

   Note that the definition referenced by sdfRef might contain qualities
   or definitions that are not valid in the context where the sdfRef is
   used.  In this case, the resulting model, when resolved, may be
   invalid.  Example: an sdfRef adds an sdfThing definition in an
   sdfObject definition.

   As a convention, overrides are intended to be used only for further
   restricting the allowable set of data values.  Such a usage is shown
   in Figure 5: any value allowable for a cable-length is also an
   allowable value for a length, with the additional restriction that
   the length cannot be smaller than 5 cm.  (This is labeled as a
   convention as it cannot be checked in the general case.  A quality of
   implementation consideration for a tool might be to provide at least
   some form of checking.)  Note that the example provides a description
   that overrides the description of the referenced definition; as this
   quality is intended for human consumption, there is no conflict with
   the intended goal.

   "sdfData":
     "length" : {
       "type": "number",
       "minimum": 0,
       "unit": "m"
       "description": "There can be no negative lengths."
     }
   ...
     "cable-length" : {
       "sdfRef": "#/sdfData/length"
       "minimum": 5e-2,
       "description": "Cables must be at least 5 cm."
     }

      Figure 5: Using an Override to Further Restrict the Set of Data
                                   Values

6.3.  sdfThing

   An sdfThing is a set of declarations and qualities that may be part
   of a more complex model.  For example, the sdfObject declarations
   that make up the definition of a single socket of an outlet strip
   could be encapsulated in an sdfThing, which itself could be used in a
   declaration in the sdfThing definition for the outlet strip.  (See
   Figure 7 in Appendix D.1 for parts of an SDF model for this example.)

   sdfThing definitions carry semantic meaning, such as a defined
   refrigerator compartment and a defined freezer compartment, making up
   a combination refrigerator-freezer product.  An sdfThing may be
   composed of sdfObjects and other sdfThings.  It can also contain
   sdfData definitions, as well as declarations of interaction
   affordances itself, such as a status (on/off) for the refrigerator-
   freezer as a whole (see Figure 8 in Appendix D.2 for an example SDF
   model illustrating these aspects).

   The qualities of sdfThing are shown in Table 10.  None of these
   qualities are required or have default values that are assumed if the
   quality is absent.  Analogous to sdfObject, the presence of one or
   both of the optional qualities "minItems" and "maxItems" defines the
   sdfThing as an array.

         +=============+===========+=============================+
         | Quality     | Type      | Description                 |
         +=============+===========+=============================+
         | (common)    |           | Section 4.6                 |
         +-------------+-----------+-----------------------------+
         | sdfThing    | thing     |                             |
         +-------------+-----------+-----------------------------+
         | sdfObject   | object    |                             |
         +-------------+-----------+-----------------------------+
         | sdfProperty | property  | zero or more named property |
         |             |           | definitions for this thing  |
         +-------------+-----------+-----------------------------+
         | sdfAction   | action    | zero or more named action   |
         |             |           | definitions for this thing  |
         +-------------+-----------+-----------------------------+
         | sdfEvent    | event     | zero or more named event    |
         |             |           | definitions for this thing  |
         +-------------+-----------+-----------------------------+
         | sdfData     | named-sdq | zero or more named data     |
         |             |           | type definitions that might |
         |             |           | be used in the above        |
         +-------------+-----------+-----------------------------+
         | minItems    | number    | (array) minimum number of   |
         |             |           | multiplied affordances in   |
         |             |           | array                       |
         +-------------+-----------+-----------------------------+
         | maxItems    | number    | (array) maximum number of   |
         |             |           | multiplied affordances in   |
         |             |           | array                       |
         +-------------+-----------+-----------------------------+

                      Table 10: Qualities of sdfThing

7.  IANA Considerations

7.1.  Media Type

   IANA has added the following Media-Type to the "Media Types" registry
   [IANA.media-types].

   +==========+======================+=======================+
   | Name     | Template             | Reference             |
   +==========+======================+=======================+
   | sdf+json | application/sdf+json | RFC 9880, Section 7.1 |
   +----------+----------------------+-----------------------+

            Table 11: Media Type Registration for SDF

   Type name:  application

   Subtype name:  sdf+json

   Required parameters:  N/A

   Optional parameters:  N/A

   Encoding considerations:  binary (JSON is UTF-8-encoded text)

   Security considerations:  Section 8 of RFC 9880

   Interoperability considerations:  none

   Published specification:  Section 7.1 of RFC 9880

   Applications that use this media type:  Tools for data and
      interaction modeling in the Internet of Things and related
      environments.

   Fragment identifier considerations:  A JSON Pointer fragment
      identifier may be used as defined in Section 6 of [RFC6901].

   Additional information:

      Magic number(s):  n/a
      File extension(s):  .sdf.json
      Windows Clipboard Name:  "Semantic Definition Format (SDF) for
         Data and Interactions of Things"
      Macintosh file type code(s):  n/a
      Macintosh Universal Type Identifier code:  org.ietf.sdf-json
         conforms to public.text

   Person & email address to contact for further information:  ASDF WG
      mailing list (asdf@ietf.org) or IETF Applications and Real-Time
      Area (art@ietf.org)

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author/Change controller:  IETF

   Provisional registration:  no

7.2.  Content-Format

   IANA has added the following Content-Format to the "CoAP Content-
   Formats" registry within the "Constrained RESTful Environments (CoRE)
   Parameters" registry group [IANA.core-parameters].

   +======================+================+=====+===========+
   | Content Type         | Content Coding | ID  | Reference |
   +======================+================+=====+===========+
   | application/sdf+json | -              | 434 | RFC 9880  |
   +----------------------+----------------+-----+-----------+

            Table 12: SDF Content-Format Registration

7.3.  IETF URN Sub-Namespace for Unit Names (urn:ietf:params:unit)

   IANA has registered the following value in the "IETF URN Sub-
   namespace for Registered Protocol Parameter Identifiers" registry in
   [IANA.params], following the template in [BCP73]:

   Registry name:  unit

   Specification:  RFC 9880

   Repository:  Combining the symbol values from the "SenML Units"
      registry and the "Secondary Units" registry in the "Sensor
      Measurement Lists (SenML)" registry group [IANA.senml] as
      specified by Sections 4.5.2 and 12.1 of [RFC8428] and Section 3 of
      [RFC8798], respectively (which, by the registration policy, are
      guaranteed to be non-overlapping).

   Index value:  Percent-encoding (Section 2.1 of RFC 3986 [STD66]) is
      required of any characters in unit names except for the set
      "unreserved" (Section 2.3 of RFC 3986 [STD66]), the set "sub-
      delims" (Section 2.2 of RFC 3986 [STD66]), and ":" or "@" (i.e.,
      the result must match the ABNF rule "pchar" in Section 3.3 of RFC
      3986 [STD66]).

7.4.  SenML Registry Group

   IANA has added the following note to the "Sensor Measurement Lists
   (SenML)" registry group [IANA.senml]:

   |  In SDF [RFC9880], a URI unit name is distinguished from a
   |  registered unit name by the presence of a colon; any registered
   |  unit name that contains a colon can therefore not be directly used
   |  in SDF.

7.5.  Registries

   IANA has created the "Semantic Definition Format (SDF)" registry
   group with the registries defined in this Section.

7.5.1.  SDF Quality Names

   IANA has created the "SDF Quality Names" registry in the "Semantic
   Definition Format (SDF)" registry group with the following template:

   Name:  A Quality Name composed of ASCII letters, digits, and dollar
      signs, starting with a lowercase ASCII letter or a dollar sign
      (i.e., using a pattern of "[a-z$][A-Za-z$0-9]*").

   Brief Description:  A brief description.

   Reference:  A pointer to a specification.

   Change Controller:  (See Section 2.3 of RFC 8126 [BCP26])

   Quality Names in this registry are intended to be registered in
   conjunction with RFCs and activities of the IETF.

   The registration policy is Specification Required as per Section 4.6
   of RFC 8126 [BCP26].  Note that the policy is not "RFC Required" or
   "IETF Review" (Sections 4.7 and 4.8 of RFC 8126 [BCP26]) so that
   registrations can be made earlier in the process, even earlier than
   foreseen in [BCP100].)

   The instructions to the Experts are:

   *  to ascertain that the specification is available in an immutable
      reference and has achieved a good level of review in conjunction
      with RFCs or activities of the IETF, and

   *  to be frugal in the allocation of Quality Names that are
      suggestive of generally applicable semantics, keeping them in
      reserve for qualities that are likely to enjoy wide use and can
      make good use of their conciseness.

   The "SDF Quality Names" registry starts out as in Table 13; all
   references for these initial entries are to RFC 9880 (this document)
   and all change controllers are "IETF".

    +======================+==========================================+
    | Name                 | Brief Description                        |
    +======================+==========================================+
    | $comment             | source code comments only, no semantics  |
    +----------------------+------------------------------------------+
    | const                | constant value                           |
    +----------------------+------------------------------------------+
    | contentFormat        | content format                           |
    +----------------------+------------------------------------------+
    | default              | default value                            |
    +----------------------+------------------------------------------+
    | description          | long description text                    |
    +----------------------+------------------------------------------+
    | enum                 | sdfChoice limited to text strings        |
    +----------------------+------------------------------------------+
    | exclusiveMaximum     | exclusive maximum for a number           |
    +----------------------+------------------------------------------+
    | exclusiveMinimum     | exclusive minimum for a number           |
    +----------------------+------------------------------------------+
    | format               | specific format for a text string        |
    +----------------------+------------------------------------------+
    | items                | items of an array                        |
    +----------------------+------------------------------------------+
    | label                | short text (no constraints); defaults to |
    |                      | key                                      |
    +----------------------+------------------------------------------+
    | maxItems             | maximum number of items in an array      |
    +----------------------+------------------------------------------+
    | maxLength            | maximum length for a text string (in     |
    |                      | characters, i.e., Unicode scalar values) |
    +----------------------+------------------------------------------+
    | maximum              | maximum for a number                     |
    +----------------------+------------------------------------------+
    | minItems             | minimum number of items in an array      |
    +----------------------+------------------------------------------+
    | minLength            | minimum length for a text string (in     |
    |                      | characters, i.e., Unicode scalar values) |
    +----------------------+------------------------------------------+
    | minimum              | minimum for a number                     |
    +----------------------+------------------------------------------+
    | multipleOf           | step size of number                      |
    +----------------------+------------------------------------------+
    | nullable             | boolean: can the item be left out?       |
    +----------------------+------------------------------------------+
    | observable           | boolean: can the item be observed?       |
    +----------------------+------------------------------------------+
    | pattern              | regular expression pattern for a text    |
    |                      | string                                   |
    +----------------------+------------------------------------------+
    | properties           | named dataqualities for type="object"    |
    +----------------------+------------------------------------------+
    | readable             | boolean: can the item be read?           |
    +----------------------+------------------------------------------+
    | required             | which data items are required?           |
    +----------------------+------------------------------------------+
    | sdfChoice            | named dataqualities for a choice         |
    +----------------------+------------------------------------------+
    | sdfData              | named dataqualities for an independent   |
    |                      | data type definition                     |
    +----------------------+------------------------------------------+
    | sdfInputData         | input data to an action                  |
    +----------------------+------------------------------------------+
    | sdfOutputData        | output data of an action or event        |
    |                      | (sdfRequired applies here)               |
    +----------------------+------------------------------------------+
    | sdfRef               | sdf-pointer to definition being          |
    |                      | referenced                               |
    +----------------------+------------------------------------------+
    | sdfRequired          | pointer-list to declarations of required |
    |                      | components                               |
    +----------------------+------------------------------------------+
    | sdfRequiredInputData | pointer-list to declarations of required |
    |                      | input data for an action                 |
    +----------------------+------------------------------------------+
    | sdfType              | more detailed information about the type |
    |                      | of a string                              |
    +----------------------+------------------------------------------+
    | type                 | general category of data type            |
    +----------------------+------------------------------------------+
    | uniqueItems          | boolean: do the items of the array need  |
    |                      | to be all different?                     |
    +----------------------+------------------------------------------+
    | unit                 | engineering unit and scale (per SenML    |
    |                      | registry)                                |
    +----------------------+------------------------------------------+
    | writable             | boolean: can the item be written to?     |
    +----------------------+------------------------------------------+

        Table 13: Initial Content of the SDF Quality Names Registry

7.5.2.  SDF Quality Name Prefixes

   IANA has created the "SDF Quality Name Prefixes" registry in the
   "Semantic Definition Format (SDF)" registry group with the following
   template:

   Prefix:  A Quality Name prefix composed of lowercase ASCII letters
      and digits, starting with a lowercase ASCII letter (i.e., using a
      pattern of "[a-z][a-z0-9]*").

   Contact:  A contact point for the organization that assigns Quality
      Names with this prefix.

   Reference:  A pointer to additional information, if available.

   Quality Name Prefixes are intended to be registered by organizations
   that plan to define Quality Names constructed with an organization-
   specific prefix (Section 2.3.3).

   The registration policy is Expert Review as per Section 4.5 of RFC
   8126 [BCP26].  The instructions to the Expert are to ascertain that
   the organization will handle Quality Names constructed using their
   prefix in a way that roughly achieves the objectives for an IANA
   registry that supports interoperability of SDF models employing these
   Quality Names, including:

   *  Stability, "stable and permanent";

   *  Transparency, "readily available" and "in sufficient detail"
      (Section 4.6 of RFC 8126 [BCP26]).

   The "SDF Quality Name Prefixes" registry is empty at this time.

7.5.3.  sdfType Values

   IANA has created the "sdfType Values" registry in the "Semantic
   Definition Format (SDF)" registry group with the following template:

   Name:  A name composed of lowercase ASCII letters, digits and -
      (ASCII hyphen/minus) characters, starting with a lowercase ASCII
      letter (i.e., using a pattern of "[a-z][-a-z0-9]*").

   Description:  A short description of the information model level
      structure and semantics.

   type:  The value of the quality "type" to be used with this sdfType.

   JSON Representation:  A short description of a JSON representation
      that can be used for this sdfType.  As per Section 4.7.1, this
      MUST be consistent with the type.

   Reference:  A more detailed specification of meaning and use of
      sdfType.

   sdfType values are intended to be registered to enable modeling
   additional SDF-specific types (see Section 4.7.1).

   The registration policy is Specification Required as per Section 4.6
   of RFC 8126 [BCP26].  The instructions to the Expert are to ascertain
   that the specification provides enough detail to enable
   interoperability between implementations of the sdfType being
   registered, and that names are chosen with enough specificity that
   ecosystem-specific sdfTypes will not be confused with more generally
   applicable ones.

   The initial set of registrations is described in Table 5.

7.5.4.  SDF Feature Names

   IANA has created the "SDF Feature Names" registry in the "Semantic
   Definition Format (SDF)" registry group with the following template:

   Name:  A feature name composed of ASCII letters, digits, and dollar
      signs, starting with a lowercase ASCII letter or a dollar sign
      (i.e., using a pattern of "[a-z$][A-Za-z$0-9]*").

   Brief Description:  A brief description.

   Reference:  A pointer to a specification.

   Change Controller:  (See Section 2.3 of RFC 8126 [BCP26])

   The registration policy is Specification Required as per Section 4.6
   of RFC 8126 [BCP26].

   The instructions to the Experts are:

   *  to ascertain that the specification is available in an immutable
      reference and has achieved a good level of review, and

   *  to be frugal in the allocation of feature names that are
      suggestive of generally applicable semantics, keeping them in
      reserve for features that are likely to enjoy wide use and can
      make good use of their conciseness.

   The "SDF Feature Names" registry is empty at this time.

8.  Security Considerations

   Some wider security considerations applicable to Things are discussed
   in [RFC8576].

   Section 5 of [RFC8610] gives an overview over security considerations
   that arise when formal description techniques are used to govern
   interoperability; analogs of these security considerations can apply
   to SDF.

   The security considerations of underlying building blocks such as
   those detailed in Section 10 of RFC 3629 [STD63] apply.

   SDF uses JSON as a representation language.  For a number of cases,
   [STD90] indicates that implementation behavior for certain constructs
   allowed by the JSON grammar is unpredictable.

   Implementations need to be robust against invalid or unpredictable
   cases on input, preferably by rejecting input that is invalid or that
   would lead to unpredictable behavior, and avoid generating these
   cases on output.

   Implementations of model languages may also exhibit performance-
   related availability issues when the attacker can control the input,
   see Section 4.1 of [RFC9535] for a brief discussion and Section 8 of
   [RFC9485] for considerations specific to the use of pattern.

   SDF may be used in two processes that are often security relevant:
   (1) model-based _validation_ of data that is intended to be described
   by SDF models, and (2) model-based _augmentation_ of these data with
   information obtained from the SDF models that apply.

   Implementations need to ascertain the provenance (and thus
   authenticity and integrity) and applicability of the SDF models they
   employ operationally in such security-relevant ways.  Implementations
   that make use of the composition mechanisms defined in this document
   need to do this for each of the components they combine into the SDF
   models they employ.  Essentially, this process needs to undergo the
   same care and scrutiny as any other introduction of source code into
   a build environment; the possibility of supply-chain attacks on the
   modules imported needs to be considered.

   Specifically, implementations might rely on model-based input
   validation for enforcing certain characteristics of the data
   structure ingested (which, if not validated, could lead to
   malfunctions such as crashes and remote code execution).  These
   implementations need to be particularly careful about the data models
   they apply, including their provenance and potential changes of these
   characteristics that upgrades to the referenced modules may
   (inadvertently or as part of an attack) cause.  More generally
   speaking, implementations should strive to be robust against expected
   and unexpected limitations of the model-based input validation
   mechanisms and their implementations.

   Similarly, implementations that rely on model-based augmentation may
   generate false data from their inputs; this is an integrity violation
   in any case, but also can possibly be exploited for further attacks.

   In applications that dynamically acquire models and obtain modules
   from module references in these models, the security considerations
   of dereferenceable identifiers apply (see [DEREF-ID-PATTERN] for a
   more extensive discussion of dereferenceable identifiers).

   There may be confidentiality requirements on SDF models, both on
   their content and on the fact that a specific model is used in a
   particular Thing or environment.  The present specification does not
   discuss model discovery or define an access control model for SDF
   models, nor does it define a way to obtain selective disclosure where
   that may be required.  It is likely that these definitions require
   additional context from underlying ecosystems and the characteristics
   of the protocols employed there; therefore, this is left as future
   work (e.g., for documents such as [SDF-MAPPING]).

9.  References

9.1.  Normative References

   [BCP26]    Best Current Practice 26,
              <https://www.rfc-editor.org/info/bcp26>.
              At the time of writing, this BCP comprises the following:

              Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [BCP73]    Best Current Practice 73,
              <https://www.rfc-editor.org/info/bcp73>.
              At the time of writing, this BCP comprises the following:

              Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
              IETF URN Sub-namespace for Registered Protocol
              Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
              2003, <https://www.rfc-editor.org/info/rfc3553>.

   [IANA.core-parameters]
              IANA, "Constrained RESTful Environments (CoRE)
              Parameters",
              <https://www.iana.org/assignments/core-parameters>.

   [IANA.media-types]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types>.

   [IANA.params]
              IANA, "Uniform Resource Name (URN) Namespace for IETF
              Use", <https://www.iana.org/assignments/params>.

   [IANA.senml]
              IANA, "Sensor Measurement Lists (SenML)",
              <https://www.iana.org/assignments/senml>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

   [RFC7396]  Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
              DOI 10.17487/RFC7396, October 2014,
              <https://www.rfc-editor.org/info/rfc7396>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8428]  Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
              Bormann, "Sensor Measurement Lists (SenML)", RFC 8428,
              DOI 10.17487/RFC8428, August 2018,
              <https://www.rfc-editor.org/info/rfc8428>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

   [RFC8798]  Bormann, C., "Additional Units for Sensor Measurement
              Lists (SenML)", RFC 8798, DOI 10.17487/RFC8798, June 2020,
              <https://www.rfc-editor.org/info/rfc8798>.

   [RFC9165]  Bormann, C., "Additional Control Operators for the Concise
              Data Definition Language (CDDL)", RFC 9165,
              DOI 10.17487/RFC9165, December 2021,
              <https://www.rfc-editor.org/info/rfc9165>.

   [RFC9193]  Keränen, A. and C. Bormann, "Sensor Measurement Lists
              (SenML) Fields for Indicating Data Value Content-Format",
              RFC 9193, DOI 10.17487/RFC9193, June 2022,
              <https://www.rfc-editor.org/info/rfc9193>.

   [RFC9562]  Davis, K., Peabody, B., and P. Leach, "Universally Unique
              IDentifiers (UUIDs)", RFC 9562, DOI 10.17487/RFC9562, May
              2024, <https://www.rfc-editor.org/info/rfc9562>.

   [SPDX]     "SPDX License List", <https://spdx.org/licenses/>.

   [STD63]    Internet Standard 63,
              <https://www.rfc-editor.org/info/std63>.
              At the time of writing, this STD comprises the following:

              Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

   [STD66]    Internet Standard 66,
              <https://www.rfc-editor.org/info/std66>.
              At the time of writing, this STD comprises the following:

              Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [STD80]    Internet Standard 80,
              <https://www.rfc-editor.org/info/std80>.
              At the time of writing, this STD comprises the following:

              Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,
              <https://www.rfc-editor.org/info/rfc20>.

   [STD90]    Internet Standard 90,
              <https://www.rfc-editor.org/info/std90>.
              At the time of writing, this STD comprises the following:

              Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [STD94]    Internet Standard 94,
              <https://www.rfc-editor.org/info/std94>.
              At the time of writing, this STD comprises the following:

              Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/info/rfc8949>.

   [W3C.NOTE-curie-20101216]
              Birbeck, M., Ed. and S. McCarron, Ed., "CURIE Syntax 1.0",
              W3C Working Group Note, 16 December 2010,
              <https://www.w3.org/TR/2010/NOTE-curie-20101216/>.

9.2.  Informative References

   [BCP100]   Best Current Practice 100,
              <https://www.rfc-editor.org/info/bcp100>.
              At the time of writing, this BCP comprises the following:

              Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <https://www.rfc-editor.org/info/rfc7120>.

   [CamelCase]
              "Camel Case", December 2014,
              <http://wiki.c2.com/?CamelCase>.

   [DEREF-ID-PATTERN]
              Bormann, C. and C. Amsüss, "The "dereferenceable
              identifier" pattern", Work in Progress, Internet-Draft,
              draft-bormann-t2trg-deref-id-06, 30 August 2025,
              <https://datatracker.ietf.org/doc/html/draft-bormann-
              t2trg-deref-id-06>.

   [ECMA-262] Ecma International, "ECMAScript 2025 Language
              Specification", 16th Edition, ECMA Standard ECMA-262, June
              2025, <https://ecma-international.org/wp-content/uploads/
              ECMA-262_16th_edition_june_2025.pdf>.

   [JSO4]     Galiegue, F., Ed., Zyp, K., Ed., and G. Court, "JSON
              Schema: core definitions and terminology", Work in
              Progress, Internet-Draft, draft-zyp-json-schema-04, 31
              January 2013, <https://datatracker.ietf.org/doc/html/
              draft-zyp-json-schema-04>.

   [JSO4V]    Zyp, K. and G. Court, "JSON Schema: interactive and non
              interactive validation", Work in Progress, Internet-Draft,
              draft-fge-json-schema-validation-00, 31 January 2013,
              <https://datatracker.ietf.org/doc/html/draft-fge-json-
              schema-validation-00>.

   [JSO7]     Wright, A., Ed., Andrews, H., Ed., Hutton, B., Ed., and G.
              Dennis, "JSON Schema: A Media Type for Describing JSON
              Documents", Work in Progress, Internet-Draft, draft-
              handrews-json-schema-02, 17 September 2019,
              <https://datatracker.ietf.org/doc/html/draft-handrews-
              json-schema-02>.

   [JSO7V]    Wright, A., Ed., Andrews, H., Ed., and B. Hutton, Ed.,
              "JSON Schema Validation: A Vocabulary for Structural
              Validation of JSON", Work in Progress, Internet-Draft,
              draft-handrews-json-schema-validation-02, 17 September
              2019, <https://datatracker.ietf.org/doc/html/draft-
              handrews-json-schema-validation-02>.

   [KebabCase]
              "Kebab Case", August 2014,
              <http://wiki.c2.com/?KebabCase>.

   [OCF]      Open Connectivity Foundation, "OCF Resource Type
              Specification", Version 2.2.7, November 2023,
              <https://openconnectivity.org/specs/
              OCF_Resource_Type_Specification.pdf>.

   [OMA]      Open Mobile Alliance, "LwM2M OBJECTS",
              <https://www.openmobilealliance.org/specifications/
              registries/objects>.

   [REST-IOT] Keränen, A., Kovatsch, M., and K. Hartke, "Guidance on
              RESTful Design for Internet of Things Systems", Work in
              Progress, Internet-Draft, draft-irtf-t2trg-rest-iot-17, 20
              October 2025, <https://datatracker.ietf.org/doc/html/
              draft-irtf-t2trg-rest-iot-17>.

   [RFC8576]  Garcia-Morchon, O., Kumar, S., and M. Sethi, "Internet of
              Things (IoT) Security: State of the Art and Challenges",
              RFC 8576, DOI 10.17487/RFC8576, April 2019,
              <https://www.rfc-editor.org/info/rfc8576>.

   [RFC9485]  Bormann, C. and T. Bray, "I-Regexp: An Interoperable
              Regular Expression Format", RFC 9485,
              DOI 10.17487/RFC9485, October 2023,
              <https://www.rfc-editor.org/info/rfc9485>.

   [RFC9535]  Gössner, S., Ed., Normington, G., Ed., and C. Bormann,
              Ed., "JSONPath: Query Expressions for JSON", RFC 9535,
              DOI 10.17487/RFC9535, February 2024,
              <https://www.rfc-editor.org/info/rfc9535>.

   [SDF-MAPPING]
              Bormann, C. and J. Romann, "Semantic Definition Format
              (SDF): Mapping files", Work in Progress, Internet-Draft,
              draft-ietf-asdf-sdf-mapping-00, 18 December 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-asdf-
              sdf-mapping-00>.

   [SDFTYPE-LINK]
              Bormann, C. and A. Keränen, "An sdfType for Links", Work
              in Progress, Internet-Draft, draft-ietf-asdf-sdftype-link-
              01, 19 December 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-asdf-
              sdftype-link-01>.

   [STD97]    Internet Standard 97,
              <https://www.rfc-editor.org/info/std97>.
              At the time of writing, this STD comprises the following:

              Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/info/rfc9110>.

   [WoT]      Kaebisch, S., Ed., McCool, M., Ed., and E. Korkan, Ed.,
              "Web of Things (WoT) Thing Description 1.1",
              W3C Recommendation, 5 December 2023,
              <https://www.w3.org/TR/2023/REC-wot-thing-
              description11-20231205/>.

   [ZCL]      "Chapter 6 - The ZigBee Cluster Library", Zigbee Wireless
              Networking, pp. 239-271,
              DOI 10.1016/b978-0-7506-8597-9.00006-9,
              ISBN 9780750685979, 2008,
              <https://doi.org/10.1016/b978-0-7506-8597-9.00006-9>.

Appendix A.  Formal Syntax of SDF

   This normative appendix describes the syntax of SDF using CDDL
   [RFC8610].

   This appendix shows the framework syntax only, i.e., a syntax with
   liberal extension points.  Since this syntax is nearly useless in
   finding typos in an SDF specification, a second syntax, the
   validation syntax, is defined that does not include the extension
   points.  The validation syntax can be generated from the framework
   syntax by leaving out all lines containing the string EXTENSION-
   POINT; as this is trivial, the result is not shown here.

   This appendix makes use of CDDL "features" as defined in Section 4 of
   [RFC9165].  Features whose names end in "-ext" indicate extension
   points for further evolution.

   start = sdf-syntax

   sdf-syntax = {
    ; info will be required in most process policies
    ? info: sdfinfo
    ? namespace: named<text>
    ? defaultNamespace: text
    ; Thing is a composition of objects that work together in some way
    ? sdfThing: named<thingqualities>
    ; Object is a set of Properties, Actions, and Events that together
    ; perform a particular function
    ? sdfObject: named<objectqualities>
    ; Includes Properties, Actions, and Events as well as sdfData
    paedataqualities
    * $$SDF-EXTENSION-TOP
    EXTENSION-POINT<"top-ext">
   }

   sdfinfo = {
    ? title: text
    ? description: text
    ? version: text
    ? copyright: text
    ? license: text
    ? modified: modified-date-time
    ? features: [
                  * (any .feature "feature-name") ; EXTENSION-POINT
                ]
    optional-comment
    * $$SDF-EXTENSION-INFO
    EXTENSION-POINT<"info-ext">
   }

   ; Shortcut for a map that gives names to instances of X
   ; (has keys of type text and values of type X)
   named<X> = { * text => X }

   ; EXTENSION-POINT is only used in framework syntax
   EXTENSION-POINT<f> = ( * (quality-name .feature f) => any )
   quality-name = text .regexp "([a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*"

   sdf-pointer = global / same-object / true
   global = text .regexp ".*[:#].*" ; rough CURIE or JSON Pointer syntax
   same-object = referenceable-name
   referenceable-name = text .regexp "[^:#]*"

   ; per se no point in having an empty list, but used for sdfRequired
   ; in odmobject-multiple_axis_joystick.sdf.json
   pointer-list = [* sdf-pointer]

   optional-comment = (
    ? $comment: text       ; source code comments only, no semantics
   )

   commonqualities = (
    ? description: text    ; long text (no constraints)
    ? label: text          ; short text (no constraints); default to key
    optional-comment
    ? sdfRef: sdf-pointer
    ; applies to qualities of properties, of data:
    ? sdfRequired: pointer-list
   )

   arraydefinitionqualities = (
    ? "minItems" => uint
    ? "maxItems" => uint
   )

   paedataqualities = (
    ; Property represents the state of an instance of an object
    ? sdfProperty: named<propertyqualities>
    ; Action invokes an application layer verb associated with an object
    ? sdfAction: named<actionqualities>
    ; Event represents an occurrence of event associated with an object
    ? sdfEvent: named<eventqualities>
    ; Data represents a piece of information that can be the state of a
    ; property or a parameter to an action or a signal in an event
    ? sdfData: named<dataqualities>

   )

   ; for building hierarchy
   thingqualities = {
    commonqualities
    ? sdfObject: named<objectqualities>
    ? sdfThing: named<thingqualities>
    paedataqualities
    arraydefinitionqualities
    * $$SDF-EXTENSION-THING
    EXTENSION-POINT<"thing-ext">
   }

   ; for single objects, or for arrays of objects
   objectqualities = {
    commonqualities
    paedataqualities
    arraydefinitionqualities
    * $$SDF-EXTENSION-OBJECT
    EXTENSION-POINT<"object-ext">
   }

   parameter-list = dataqualities

   actionqualities = {
    commonqualities
    ? sdfInputData: parameter-list   ; sdfRequiredInputData applies here
    ? sdfOutputData: parameter-list  ; sdfRequired applies here
    ; zero or more named data type definitions that might be used above
    ? sdfData: named<dataqualities>
    * $$SDF-EXTENSION-ACTION
    EXTENSION-POINT<"action-ext">
   }

   eventqualities = {
    commonqualities
    ? sdfOutputData: parameter-list  ; sdfRequired applies here
    ; zero or more named data type definitions that might be used above
    ? sdfData: named<dataqualities>
    * $$SDF-EXTENSION-EVENT
    EXTENSION-POINT<"event-ext">
   }

   sdftype-name = text .regexp "[a-z][-a-z0-9]*"       ; EXTENSION-POINT

   dataqualities = {
    commonqualities
    jsonschema
    ? "unit" => text
    ? nullable: bool
    ? "sdfType" => "byte-string" / "unix-time"
               / $SDF-EXTENSION-SDFTYPE .within sdftype-name
               / (sdftype-name .feature "sdftype-ext") ; EXTENSION-POINT
    ? contentFormat: text
    * $$SDF-EXTENSION-DATA
    EXTENSION-POINT<"data-ext">
   }

   propertyqualities = {
    ? observable: bool
    ? readable: bool
    ? writable: bool
    * $$SDF-EXTENSION-PROPERTY
    ~dataqualities
   }

   allowed-types = number / text / bool / null
                 / [* number] / [* text] / [* bool]
                 / {* text => any}
                 / $SDF-EXTENSION-ALLOWED
                 / (any .feature "allowed-ext")        ; EXTENSION-POINT

   compound-type = (
     "type" => "object"
     ? required: [+text]
     ? properties: named<dataqualities>
   )

   optional-choice = (
    ? (("sdfChoice" => named<dataqualities>)
     // ("enum" => [+ text])) ; limited to text strings
   )

   jsonschema = (
    ? (("type" => "number" / "string" / "boolean" / "integer" / "array")
       // compound-type
       // $$SDF-EXTENSION-TYPE
       // (type: text .feature "type-ext")             ; EXTENSION-POINT
      )
    ; if present, all other qualities apply to all choices:
    optional-choice
    ; the next three should validate against type:
    ? const: allowed-types
    ? default: allowed-types
    ; number/integer constraints
    ? minimum: number
    ? maximum: number
    ? exclusiveMinimum: number
    ? exclusiveMaximum: number
    ? multipleOf: number
    ; text string constraints
    ? minLength: uint
    ? maxLength: uint
    ? pattern: text                ; regexp
    ? format: "date-time" / "date" / "time"
              / "uri" / "uri-reference" / "uuid"
              / $SDF-EXTENSION-FORMAT .within text
              / (text .feature "format-ext")           ; EXTENSION-POINT
    ; array constraints
    ? minItems: uint
    ? maxItems: uint
    ? uniqueItems: bool
    ? items: jso-items
   )

   jso-items = {
        ? sdfRef: sdf-pointer ; import limited to subset allowed here...
        ? description: text   ; long text (no constraints)
        optional-comment
        ; leave commonqualities out for non-complex data types,
        ; but need the above three.
        ; no further nesting: no "array"
        ? ((type: "number" / "string" / "boolean" / "integer")
           // compound-type
           // $$SDF-EXTENSION-ITEMTYPE
           // (type: text .feature "itemtype-ext")     ; EXTENSION-POINT
          )
        ; if present, all other qualities apply to all choices
        optional-choice
        ; jso subset
        ? minimum: number
        ? maximum: number
        ? format: text
        ? minLength: uint
        ? maxLength: uint
        * $$SDF-EXTENSION-ITEMS
        EXTENSION-POINT<"items-ext">
      }

   modified-date-time = text .abnf modified-dt-abnf
   modified-dt-abnf = "modified-dt" .det rfc3339z

   ; RFC 3339 sans time-numoffset, slightly condensed
   rfc3339z = '
      date-fullyear   = 4DIGIT
      date-month      = 2DIGIT  ; 01-12
      date-mday       = 2DIGIT  ; 01-28, 01-29, 01-30, 01-31 based on
                                ; month/year
      time-hour       = 2DIGIT  ; 00-23
      time-minute     = 2DIGIT  ; 00-59
      time-second     = 2DIGIT  ; 00-58, 00-59, 00-60 based on leap sec
                                ; rules
      time-secfrac    = "." 1*DIGIT
      DIGIT           =  %x30-39 ; 0-9

      partial-time    = time-hour ":" time-minute ":" time-second
                        [time-secfrac]
      full-date       = date-fullyear "-" date-month "-" date-mday

      modified-dt     = full-date ["T" partial-time "Z"]
   '

Appendix B.  json-schema.org Rendition of SDF Syntax

   This informative appendix describes the syntax of SDF defined in
   Appendix A, but uses a version of the description techniques
   advertised on json-schema.org [JSO7] [JSO7V].

   The appendix shows both the validation and the framework syntax.
   Since most of the lines are the same between these two files, those
   lines are shown only once, with a leading space, in the form of a
   unified diff.  Lines leading with a - are part of the validation
   syntax and lines leading with a + are part of the framework syntax.

    {
   -  "title": "sdf-validation.cddl -- Generated: 2025-10-13T08:43:18Z",
   +  "title": "sdf-framework.cddl -- Generated: 2025-10-13T08:43:29Z",
      "$schema": "http://json-schema.org/draft-07/schema#",
      "$ref": "#/definitions/sdf-syntax",
      "definitions": {
        "sdf-syntax": {
          "type": "object",
          "properties": {
            "info": {
              "$ref": "#/definitions/sdfinfo"
            },
            "namespace": {
              "type": "object",
              "additionalProperties": {
                "type": "string"
              }
            },
            "defaultNamespace": {
              "type": "string"
            },
            "sdfThing": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/thingqualities"
              }
            },
            "sdfObject": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/objectqualities"
              }
            },
            "sdfProperty": {
              "$ref": "#/definitions/sdfProperty-"
            },
            "sdfAction": {
              "$ref": "#/definitions/sdfAction-"
            },
            "sdfEvent": {
              "$ref": "#/definitions/sdfEvent-"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +      },
          "additionalProperties": false
        },
        "sdfinfo": {
          "type": "object",
          "properties": {
            "title": {
              "type": "string"
            },
            "description": {
              "type": "string"
            },
            "version": {
              "type": "string"
            },
            "copyright": {
              "type": "string"
            },
            "license": {
              "type": "string"
            },
            "modified": {
              "$ref": "#/definitions/modified-date-time"
            },
            "features": {
   -          "type": "array",
   -          "maxItems": 0
   +          "type": "array"
            },
            "$comment": {
              "type": "string"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +      },
          "additionalProperties": false
        },
        "modified-date-time": {
          "type": "string"
        },
        "thingqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfObject": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/objectqualities"
              }
            },
            "sdfThing": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/thingqualities"
              }
            },
            "sdfProperty": {
              "$ref": "#/definitions/sdfProperty-"
            },
            "sdfAction": {
              "$ref": "#/definitions/sdfAction-"
            },
            "sdfEvent": {
              "$ref": "#/definitions/sdfEvent-"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            },
            "minItems": {
              "$ref": "#/definitions/uint"
            },
            "maxItems": {
              "$ref": "#/definitions/uint"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +      },
          "additionalProperties": false
        },
        "sdf-pointer": {
          "anyOf": [
            {
              "$ref": "#/definitions/global"
            },
            {
              "$ref": "#/definitions/same-object"
            },
            {
              "$ref": "#/definitions/true"
            }
          ]
        },
        "global": {
          "type": "string",
          "pattern": "^[^\\n\\r]*[:#][^\\n\\r]*$"
        },
        "same-object": {
          "$ref": "#/definitions/referenceable-name"
        },
        "referenceable-name": {
          "type": "string",
          "pattern": "^[^:#]*$"
        },
        "true": {
          "type": "boolean",
          "const": true
        },
        "pointer-list": {
          "type": "array",
          "items": {
            "$ref": "#/definitions/sdf-pointer"
          }
        },
        "objectqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfProperty": {
              "$ref": "#/definitions/sdfProperty-"
            },
            "sdfAction": {
              "$ref": "#/definitions/sdfAction-"
            },
            "sdfEvent": {
              "$ref": "#/definitions/sdfEvent-"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            },
            "minItems": {
              "$ref": "#/definitions/uint"
            },
            "maxItems": {
              "$ref": "#/definitions/uint"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +      },
          "additionalProperties": false
        },
        "propertyqualities": {
          "anyOf": [
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +          },
              "properties": {
                "type": {
                  "$ref": "#/definitions/type-"
                },
                "sdfChoice": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "observable": {
                  "type": "boolean"
                },
                "readable": {
                  "type": "boolean"
                },
                "writable": {
                  "type": "boolean"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +          },
              "properties": {
                "type": {
                  "type": "string",
                  "const": "object"
                },
                "required": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "properties": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "sdfChoice": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "observable": {
                  "type": "boolean"
                },
                "readable": {
                  "type": "boolean"
                },
                "writable": {
                  "type": "boolean"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +          },
   +          "properties": {
   +            "type": {
   +              "type": "string"
   +            },
   +            "sdfChoice": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   +            },
   +            "observable": {
   +              "type": "boolean"
   +            },
   +            "readable": {
   +              "type": "boolean"
   +            },
   +            "writable": {
   +              "type": "boolean"
   +            },
   +            "description": {
   +              "type": "string"
   +            },
   +            "label": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "sdfRef": {
   +              "$ref": "#/definitions/sdf-pointer"
   +            },
   +            "sdfRequired": {
   +              "$ref": "#/definitions/pointer-list"
   +            },
   +            "const": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "default": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "minimum": {
   +              "type": "number"
   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "exclusiveMinimum": {
   +              "type": "number"
   +            },
   +            "exclusiveMaximum": {
   +              "type": "number"
   +            },
   +            "multipleOf": {
   +              "type": "number"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "pattern": {
   +              "type": "string"
   +            },
   +            "format": {
   +              "$ref": "#/definitions/format-"
   +            },
   +            "minItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "uniqueItems": {
   +              "type": "boolean"
   +            },
   +            "items": {
   +              "$ref": "#/definitions/jso-items"
   +            },
   +            "unit": {
   +              "type": "string"
   +            },
   +            "nullable": {
   +              "type": "boolean"
   +            },
   +            "sdfType": {
   +              "$ref": "#/definitions/sdfType-"
   +            },
   +            "contentFormat": {
   +              "type": "string"
   +            }
   +          },
   +          "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +          },
              "properties": {
                "type": {
                  "$ref": "#/definitions/type-"
                },
                "enum": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "observable": {
                  "type": "boolean"
                },
                "readable": {
                  "type": "boolean"
                },
                "writable": {
                  "type": "boolean"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +          },
              "properties": {
                "type": {
                  "type": "string",
                  "const": "object"
                },
                "required": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "properties": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "enum": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "observable": {
                  "type": "boolean"
                },
                "readable": {
                  "type": "boolean"
                },
                "writable": {
                  "type": "boolean"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +          },
   +          "properties": {
   +            "type": {
   +              "type": "string"
   +            },
   +            "enum": {
   +              "type": "array",
   +              "items": {
   +                "type": "string"
   +              },
   +              "minItems": 1
   +            },
   +            "observable": {
   +              "type": "boolean"
   +            },
   +            "readable": {
   +              "type": "boolean"
   +            },
   +            "writable": {
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   +            "description": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "minimum": {
   +              "type": "number"
   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "format": {
   +              "type": "string"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            }
   +          },
   +          "additionalProperties": false
            }
          ]
        },
   +    "sdftype-name": {
   +      "type": "string",
   +      "pattern": "^[a-z][\\-a-z0-9]*$"
   +    },
        "actionqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfInputData": {
              "$ref": "#/definitions/parameter-list"
            },
            "sdfOutputData": {
              "$ref": "#/definitions/parameter-list"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +      },
          "additionalProperties": false
        },
        "parameter-list": {
          "$ref": "#/definitions/dataqualities"
        },
        "eventqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfOutputData": {
              "$ref": "#/definitions/parameter-list"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {}
   +      },
          "additionalProperties": false
        },
        "format-": {
   -      "type": "string",
   -      "enum": [
   -        "date-time",
   -        "date",
   -        "time",
   -        "uri",
   -        "uri-reference",
   -        "uuid"
   +      "anyOf": [
   +        {
   +          "type": "string",
   +          "const": "date-time"
   +        },
   +        {
   +          "type": "string",
   +          "const": "date"
   +        },
   +        {
   +          "type": "string",
   +          "const": "time"
   +        },
   +        {
   +          "type": "string",
   +          "const": "uri"
   +        },
   +        {
   +          "type": "string",
   +          "const": "uri-reference"
   +        },
   +        {
   +          "type": "string",
   +          "const": "uuid"
   +        },
   +        {
   +          "type": "string"
   +        }
   +      ]
   +    },
   +    "sdfType-": {
   +      "anyOf": [
   +        {
   +          "type": "string",
   +          "const": "byte-string"
   +        },
   +        {
   +          "type": "string",
   +          "const": "unix-time"
   +        },
   +        {
   +          "$ref": "#/definitions/sdftype-name"
   +        }
          ]
        },
        "sdfData-sdfChoice-properties-": {
          "type": "object",
          "additionalProperties": {
            "$ref": "#/definitions/dataqualities"
          }
        },
        "type-": {
          "type": "string",
          "enum": [
            "number",
            "string",
            "boolean",
            "integer",
            "array"
          ]
        },
   -    "sdfEvent-": {
   +    "sdfProperty-": {
          "type": "object",
          "additionalProperties": {
   -        "$ref": "#/definitions/eventqualities"
   +        "$ref": "#/definitions/propertyqualities"
          }
        },
        "sdfAction-": {
          "type": "object",
          "additionalProperties": {
            "$ref": "#/definitions/actionqualities"
          }
        },
   -    "sdfProperty-": {
   +    "sdfEvent-": {
          "type": "object",
          "additionalProperties": {
   -        "$ref": "#/definitions/propertyqualities"
   +        "$ref": "#/definitions/eventqualities"
          }
   -    },
   -    "sdfType-": {
   -      "type": "string",
   -      "enum": [
   -        "byte-string",
   -        "unix-time"
   -      ]
        }
      }
    }

Appendix C.  Data Qualities Inspired by json-schema.org

   This appendix is normative.

   Data qualities define data used in SDF affordances at an information
   model level.  A popular way to describe JSON data at a data model
   level is proposed by a number of drafts on json-schema.org (which
   collectively are abbreviated JSO here); for reference to a popular
   version, this appendix points to [JSO7] and [JSO7V].  As the
   vocabulary used by JSO is familiar to many JSON modelers, the present
   specification borrows some of the terms and ports their semantics to
   the information model level needed for SDF.

   The main data quality imported is the "type".  In SDF, this can take
   one of six (text string) values, which are discussed in the following
   subsections (note that the JSO type "null" is not supported as a
   value of this data quality in SDF).

   The additional quality "const" restricts the data to one specific
   value (given as the value of the const quality).

   Similarly, the additional quality "default" provides data that can be
   used in the absence of the data (given as the value of the default
   quality); this is mainly documentary and not very well-defined for
   SDF as no process is defined that would add default values to an
   instance of some interaction data.

   Other qualities that are inspired by JSO are "$comment" and
   "description", both of which are also available in the information
   block.

C.1.  type "number", type "integer"

   The types "number" and "integer" are associated with floating point
   and integer numbers, as they are available in JSON.  A type value of
   integer means that only integer values of JSON numbers can be used
   (note that 10.0 is an integer value, even if it is in a notation that
   would also allow non-zero decimal fractions).

   The additional data qualities "minimum", "maximum",
   "exclusiveMinimum", and "exclusiveMaximum" provide number values that
   serve as inclusive/exclusive lower/upper bounds for the number.
   (Note that the Boolean form of "exclusiveMinimum"/"exclusiveMaximum"
   found in earlier JSO drafts [JSO4V] is not used.)

   The data quality "multipleOf" gives a positive number that constrains
   the data value to be an integer multiple of the number given.  (Type
   "integer" can also be expressed as a "multipleOf" quality of value 1,
   unless another "multipleOf" quality is present.)

C.2.  type "string"

   The type "string" is associated with Unicode text string values, as
   they can be represented in JSON.

   The length (as measured in characters, specifically Unicode scalar
   values) can be constrained by the additional data qualities
   "minLength" and "maxLength", which are inclusive bounds.

   (More specifically, Unicode text strings as defined in this
   specification are sequences of Unicode scalar values, the number of
   which is taken as the length of such a text string.

   The data quality "pattern" takes a string value that is interpreted
   as an [ECMA-262] regular expression in Unicode mode that constrains
   the string (note that these are not anchored by default, so unless ^
   and $ anchors are employed, ECMA-262 regular expressions match any
   string that _contains_ a match).  The JSO proposals acknowledge that
   regular expression support is rather diverse in various platforms, so
   the suggestion is to limit them to:

   *  characters;
   *  character classes in square brackets, including ranges; their
      complements;
   *  simple quantifiers *, +, ?, and range quantifiers {n}, {n,m}, and
      {n,};
   *  grouping parentheses;
   *  the choice operator |;
   *  and anchors (beginning-of-input ^ and end-of-input $).

   Note that this subset is somewhat similar to the subset introduced by
   I-Regexps [RFC9485], which are anchored regular expressions and
   include certain backslash escapes for characters and character
   classes.

   The additional data quality "format" can take one of the following
   values.  Note that, at an information model level, the presence of
   this data quality changes the type from being a simple text string to
   the abstract meaning of the format given (i.e., the format "date-
   time" is less about the specific syntax employed in [RFC3339] than
   about the usage as an absolute point in civil time).

   *  "date-time", "date", "time": A date-time, full-date, or full-time
      as defined in [RFC3339], respectively.
   *  "uri", "uri-reference": A URI or URI Reference as defined in
      [STD66], respectively.
   *  "uuid": A Universally Unique Identifier (UUID) as defined in
      [RFC9562]).

C.3.  type "boolean"

   The type "boolean" can take the values "true" or "false".

C.4.  type "array"

   The type "array" is associated with arrays, as they are available in
   JSON.

   The additional quality "items" gives the type that each of the
   elements of the array must match.

   The number of elements in the array can be constrained by the
   additional data qualities "minItems" and "maxItems", which are
   inclusive bounds.

   The additional data quality "uniqueItems" gives a Boolean value that,
   if true, requires the elements to be all different.

C.5.  type "object"

   The type "object" is associated with maps, from strings to values, as
   they are available in JSON.

   The additional quality "properties" is a map the entries of which
   describe entries in the specified JSON map: the key gives an
   allowable map key for the specified JSON map and the value is a map
   with a named set of data qualities giving the type for the
   corresponding value in the specified JSON map.

   All entries specified in this way are optional unless they are listed
   in the value of the additional quality "required", which is an array
   of string values that give the key names of required entries.

   Note that the term "properties" as an additional quality for defining
   map entries is unrelated to sdfProperty.

   For example, to include information about the type of the event in
   the "overTemperatureEvent" of Figure 4, the sdfOutputData there could
   be defined as follows:

       "sdfOutputData": {
         "type": "object",
         "properties": {
           "alarmType": {
             "sdfRef": "cap:#/sdfData/alarmTypes/quantityAlarms",
             "const": "OverTemperatureAlarm"
           },
           "temperature": {
   "sdfRef": "#/sdfObject/temperatureWithAlarm/sdfData/temperatureData"
           }
         }
       }

               Figure 6: Using Object Type with sdfOutputData

C.6.  Implementation Notes

   JSO-based keywords are also used in the specification techniques of a
   number of ecosystems, but some adjustments may be required.

   For instance, [OCF] is based on Swagger 2.0, which appears to be
   based on "draft-4" [JSO4] [JSO4V] (also called draft-5, but
   semantically intended to be equivalent to draft-4).  The
   "exclusiveMinimum" and "exclusiveMaximum" keywords use the Boolean
   form there, so on import to SDF, their values have to be replaced by
   the values of the respective "minimum"/"maximum" keyword, which are
   then removed; the reverse transformation applies on export.

Appendix D.  Composition Examples

   This informative appendix contains two examples illustrating
   different composition approaches using the sdfThing quality.

D.1.  Outlet Strip Example

   {
     "sdfThing": {
       "outlet-strip": {
         "label": "Outlet strip",
         "description": "Contains a number of Sockets",
         "sdfObject": {
           "socket": {
             "description": "An array of sockets in the outlet strip",
             "minItems": 2,
             "maxItems": 10
           }
         }
       }
     }
   }

                       Figure 7: Outlet Strip Example

D.2.  Refrigerator-Freezer Example

   {
     "sdfThing": {
       "refrigerator-freezer": {
         "description": "A refrigerator combined with a freezer",
         "sdfProperty": {
           "status": {
             "type": "boolean",
             "description":
   "Indicates if the refrigerator-freezer is powered"
           }
         },
         "sdfObject": {
           "refrigerator": {
             "description": "A refrigerator compartment",
             "sdfProperty": {
               "temperature": {
                 "sdfRef": "#/sdfProperty/temperature",
                 "maximum": 8
               }
             }
           },
           "freezer": {
             "label": "A freezer compartment",
             "sdfProperty": {
               "temperature": {
                 "sdfRef": "#/sdfProperty/temperature",
                 "maximum": -6
               }
             }
           }
         }
       }
     },
     "sdfProperty": {
       "temperature": {
         "description": "The temperature for this compartment",
         "type": "number",
         "unit": "Cel"
       }
     }
   }

                   Figure 8: Refrigerator-Freezer Example

Appendix E.  Some Changes from Earlier Draft Versions of this
             Specification

   This appendix is informative.

   The present document provides the base SDF definition.  Previous
   revisions of SDF, as defined in earlier drafts of this specification,
   have been in use for several years; both significant collections of
   older SDF models and older SDF conversion tools are available today.
   This appendix provides a brief checklist that can aid in upgrading
   these to the standard.

   *  The quality unit was previously called units.

   *  sdfType was developed out of a concept previously called subtype.

   *  sdfChoice is the preferred way to represent JSO enum (only a
      limited form of which is retained) and also the way to represent
      JSO anyOf.

   *  The length of text strings (as used with minLength/maxLength
      constraints) was previously defined in bytes.  It now is defined
      as the number of characters (Unicode scalar values, to be exact);
      a length in bytes is not meaningful unless bound to a specific
      encoding, which might differ from UTF-8 in some ecosystem mappings
      and protocol bindings.

List of Figures

   Figure 1:  A Simple Example of an SDF Document
   Figure 2:  Main Classes Used in SDF Models
   Figure 3:  Example sdfObject Definition
   Figure 4:  Using sdfRequired
   Figure 5:  Using an Override to Further Restrict the Set of Data
              Values
   Figure 6:  Using Object Type with sdfOutputData
   Figure 7:  Outlet Strip Example
   Figure 8:  Refrigerator-Freezer Example

List of Tables

   Table 1:   Qualities of the Information Block
   Table 2:   Namespaces Block
   Table 3:   Common Qualities
   Table 4:   SDF-Defined Qualities of sdfData and sdfProperty
   Table 5:   Values Defined in Base SDF for the sdfType Quality
   Table 6:   Qualities of sdfObject
   Table 7:   Qualities of sdfProperty
   Table 8:   Qualities of sdfAction
   Table 9:   Qualities of sdfEvent
   Table 10:  Qualities of sdfThing
   Table 11:  Media Type Registration for SDF
   Table 12:  SDF Content-Format Registration
   Table 13:  Initial Content of the SDF Quality Names Registry

Acknowledgements

   This specification is based on work by the One Data Model group.

Contributors

   Jan Romann
   Universität Bremen
   Germany
   Email: jan.romann@uni-bremen.de


   Wouter van der Beek
   Cascoda Ltd.
   Threefield House
   Threefield Lane
   Southampton
   United Kingdom
   Email: w.vanderbeek@cascoda.com


Authors' Addresses

   Michael Koster (editor)
   KTC Control AB
   29415 Alderpoint Road
   Blocksburg, CA 95514
   United States of America
   Phone: +1-707-502-5136
   Email: michaeljohnkoster@gmail.com


   Carsten Bormann (editor)
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany
   Phone: +49-421-218-63921
   Email: cabo@tzi.org


   Ari Keränen
   Ericsson
   FI-02420 Jorvas
   Finland
   Email: ari.keranen@ericsson.com
