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T2TRG                                                     M. Koster, Ed.
Internet-Draft                                               SmartThings
Intended status: Informational                           C. Bormann, Ed.
Expires: 7 December 2020                          Universität Bremen TZI
                                                             5 June 2020


  Semantic Definition Format (SDF) for Data and Interactions of Things
                        draft-onedm-t2trg-sdf-00

Abstract

   The Semantic Definition Format (SDF) is a format for domain experts
   to use in the creation and maintenance of data and interaction models
   in the Internet of Things.  It was created as a common language for
   use in the development of the One Data Model liaison organization
   (OneDM) definitions.  Tools convert this format to database formats
   and other serializations as needed.

   An SDF specification describes definitions of SDF Objects and their
   associated interactions (Events, Actions, Properties), as well as the
   Data types for the information exchanged in those interactions.

   A JSON format representation of SDF 1.0 is defined in this document.

Contributing

   Recent versions of this document are available at its GitHub
   repository https://github.com/one-data-model/sdf (https://github.com/
   one-data-model/sdf) -- this also provides an issue tracker as well as
   a way to supply "pull requests".

   General discussion of this SDF Internet-Draft for now will be on the
   mailing list of the Thing-to-Thing Research group, t2trg@irtf.org
   (subscribe at https://www.irtf.org/mailman/listinfo/t2trg
   (https://www.irtf.org/mailman/listinfo/t2trg)).

   The IRTF Note Well applies (https://www.ietf.org/about/note-well/
   (https://www.ietf.org/about/note-well/)).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.







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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology and Conventions . . . . . . . . . . . . . . .   3
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Example Definition  . . . . . . . . . . . . . . . . . . .   6
     2.2.  Elements of an SDF model  . . . . . . . . . . . . . . . .   7
       2.2.1.  sdfObject . . . . . . . . . . . . . . . . . . . . . .   9
       2.2.2.  sdfProperty . . . . . . . . . . . . . . . . . . . . .  10
       2.2.3.  sdfAction . . . . . . . . . . . . . . . . . . . . . .  11
       2.2.4.  sdfEvent  . . . . . . . . . . . . . . . . . . . . . .  11
       2.2.5.  sdfData . . . . . . . . . . . . . . . . . . . . . . .  12
       2.2.6.  sdfThing  . . . . . . . . . . . . . . . . . . . . . .  12
       2.2.7.  sdfProduct  . . . . . . . . . . . . . . . . . . . . .  13
   3.  SDF structure . . . . . . . . . . . . . . . . . . . . . . . .  13
     3.1.  Information block . . . . . . . . . . . . . . . . . . . .  13
     3.2.  Namespaces section  . . . . . . . . . . . . . . . . . . .  14
     3.3.  Definitions section . . . . . . . . . . . . . . . . . . .  15
   4.  Names and namespaces  . . . . . . . . . . . . . . . . . . . .  16
     4.1.  Structure . . . . . . . . . . . . . . . . . . . . . . . .  16
     4.2.  Contributing global names . . . . . . . . . . . . . . . .  16
     4.3.  Referencing global names  . . . . . . . . . . . . . . . .  17



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     4.4.  sdfRef  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     4.5.  sdfRequired . . . . . . . . . . . . . . . . . . . . . . .  18
       4.5.1.  Optionality using the keyword "sdfRequired" . . . . .  18
     4.6.  Common Qualities  . . . . . . . . . . . . . . . . . . . .  19
     4.7.  Data Qualities  . . . . . . . . . . . . . . . . . . . . .  20
   5.  Keywords for definition groups  . . . . . . . . . . . . . . .  22
     5.1.  sdfObject . . . . . . . . . . . . . . . . . . . . . . . .  23
     5.2.  sdfProperty . . . . . . . . . . . . . . . . . . . . . . .  23
     5.3.  sdfAction . . . . . . . . . . . . . . . . . . . . . . . .  23
     5.4.  sdfEvent  . . . . . . . . . . . . . . . . . . . . . . . .  24
     5.5.  sdfData . . . . . . . . . . . . . . . . . . . . . . . . .  25
   6.  High Level Composition  . . . . . . . . . . . . . . . . . . .  25
     6.1.  Paths in the model namespaces . . . . . . . . . . . . . .  26
     6.2.  Modular Composition . . . . . . . . . . . . . . . . . . .  26
       6.2.1.  Use of the "sdfRef" keyword to re-use a definition  .  26
     6.3.  sdfThing  . . . . . . . . . . . . . . . . . . . . . . . .  27
     6.4.  sdfProduct  . . . . . . . . . . . . . . . . . . . . . . .  28
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  28
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  29
   Appendix A.  Formal Syntax of SDF . . . . . . . . . . . . . . . .  30
   Appendix B.  json-schema.org Rendition of SDF Syntax  . . . . . .  33
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  50
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  50
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  50

1.  Introduction

   The Semantic Definition Format (SDF) is a format for domain experts
   to use in the creation and maintenance of data and interaction models
   in the Internet of Things.  It was created as a common language for
   use in the development of the One Data Model liaison organization
   (OneDM) definitions.  Tools convert this format to database formats
   and other serializations as needed.

   An SDF specification describes definitions of SDF Objects and their
   associated interactions (Events, Actions, Properties), as well as the
   Data types for the information exchanged in those interactions.

   A JSON format representation of SDF 1.0 is defined in this document.

1.1.  Terminology and Conventions









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   Thing:  A physical device that is also made available in the Internet
      of Things.  The term is used here for Things that are notable for
      their interaction with the physical world beyond interaction with
      humans; a temperature sensor or a light might be a Thing, but a
      router that employs both temperature sensors and indicator lights
      might exhibit less Thingness, as the effects of its functioning
      are mostly on the digital side.

   Affordance:  An element of an interface offered for interaction,
      defining its possible uses or making clear how it can or should be
      used.  The term is used here for the digital interfaces of a Thing
      only; it might also have physical affordances such as buttons,
      dials, and displays.

   Quality:  A metadata item in a definition or declaration which says
      something about that definition or declaration.  A quality is
      represented in SDF as an entry in a JSON map (object) that serves
      as a definition or declaration.

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

   Block:  One or more entries in a JSON map that is part of an SDF
      specification; these entries together serve a specific function.

   Group:  An entry in the main SDF map and in certain nested
      definitions that either has a Class Name Keyword as its key and a
      map of definition entries (Definition Group) or a Parameter Name
      Keyword as its key and an array of SDF pointers as a value
      (Parameter Group).

   Class Name Keyword:  One of sdfThing, sdfProduct, 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.

   Property:  An affordance that can potentially be used to read, write,
      and/or observe state on an Object.  (Note that Entries are often
      called properties in other environments; in this document, the
      term Property is specifically reserved for affordances, even if
      the map key "properties" might be imported from a data definition
      language with the other semantics.)

   Action:  An affordance that can potentially be used to perform a
      named operation on an Object.




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   Event:  An affordance that can potentially be used to obtain
      information about what happened to an Object.

   Object:  A grouping of Property, Action, and Event definitions; the
      main "atom" of reusable semantics for model construction.  (Note
      that JSON maps are often called JSON objects due to JSON's
      JavaScript heritage; properties in other environments; in this
      document, the term Object is specifically reserved for the above
      grouping, even if the type name "object" might be imported from a
      data definition language with the other semantics.)

   Parameter name keyword:  One of sdfInputData, sdfOutputData,
      sdfRequiredInputData, or sdfRequired.

   Element:  A part or an aspect of something abstract; used here in its
      usual English definition.  (Occasionally, also used specifically
      for the elements of JSON arrays.)

   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.

   Declaration:  A reference to and a use of a definition within an
      enclosing definition, intended to create component instances
      within that enclosing definition.  Every declaration can also be
      used as a definition for reference in a different place.

   Protocol Binding:  A companion document to an SDF specification that
      defines how to map the abstract concepts in the specification into
      the protocols in use in a specific ecosystem.  Might supply URL
      components, numeric IDs, and similar details.

   Conventions:

   *  The singular form is chosen as the preferred one for the keywords
      defined here.

   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







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2.1.  Example Definition

   We start with an example for the SDF definition of a simple Object
   called "Switch" (Figure 1).

   {
       "info": {
           "title": "Example file for OneDM 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 on; 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 definition file











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   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 first retrieving the
   current value and then applying/setting the inverted value.

   The "sdfObject" group lists the affordances of instances of this
   object.  The "sdfProperty" group lists the property affordances
   described by the model; these represent various perspectives on the
   state of the object.  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 [I-D.irtf-t2trg-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.)

2.2.  Elements of an SDF model

   The SDF language uses seven predefined Class Name Keywords for
   modeling connected Things, six of which are illustrated in Figure 2
   and Figure 3 (the seventh class "sdfProduct" is exactly like
   "sdfThing").



















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                   +--------+
                   |sdfThing|
                   |--------|
                   |--------|
                   +--------+
                        |
                        |
                  +---------+
                  |sdfObject|
                  |---------|
                  |---------|
                  +---------+
                        |
   +-----------+  +---------+   +--------+
   |sdfProperty|  |sdfAction|   |sdfEvent|
   |-----------|  |---------|   |--------|
   |-----------|  |---------|   |--------|
   +-----------+  +---------+   +--------+


                   +-------+
                   |sdfData|
                   |-------|
                   |-------|
                   +-------+

                 Figure 2: Main classes used in SDF models
























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   sdfThing --> "0+" sdfObject : hasObject
   sdfThing --> "0+" sdfThing : hasThing

   sdfObject --> "0+" sdfProperty : hasProperty
   sdfObject --> "0+" sdfAction : hasAction
   sdfObject --> "0+" sdfEvent : hasEvent

   sdfAction --> "1+" sdfData : hasInputData
   sdfAction --> "0+" sdfData : hasOutputData

   sdfEvent --> "1+" sdfData : hasOutputData

   sdfProperty --> "1" sdfData : isInstanceOf

   class sdfThing {
   }

   class sdfObject {
   }

   class sdfProperty {
   }

   class sdfAction {
   }

   class sdfEvent {
   }

   class sdfData {
   }

       Figure 3: Main classes used in SDF models and their relations

   The seven main Class Name Keywords are discussed below.

2.2.1.  sdfObject

   Objects, the items listed in an "sdfObject" group, are the main
   "atom" of reusable semantics for model construction.  It aligns in
   scope with common definition items from many IoT modeling systems,
   for example ZigBee Clusters [ZCL], OMA SpecWorks LwM2M Objects [OMA],
   and OCF Resource Types [OCF].

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




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   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 may different kinds of
   Things that require on/off control.

2.2.2.  sdfProperty

   "sdfProperty" is used to model elements of state within "sdfObject"
   instances.

   An instance of "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 definitions in
   "sdfData" groups, however, they actually also declare a Property with
   the given qualities to be potentially present in the containing
   Object.  (Qualities beyond those of "sdfData" definitions could be
   defined for "sdfProperty" declarations but currently aren't; this
   means that even Property qualities such as "readable" and "writable"
   can be associated with definitions in "sdfData" groups, as well.)

   For definitions in "sdfProperty" and "sdfData", SDF provides
   qualities that can constrain the structure and values of data allowed
   in an instance of these data, as well as qualities that associate
   semantics to these data, for engineering units and unit scaling
   information.

   For the data definition within "sdfProperty" or "sdfData", SDF
   borrows a number of elements proposed for the drafts 4 and 7 of the
   json-schema.org "JSON Schema" format
   [I-D.handrews-json-schema-validation], enhanced by qualities that are
   specific to SDF.  However, for the current version of SDF, data are
   constrained to be of simple types (number, string, Boolean) and
   arrays of these types.  Syntax extension points are provided that can
   be used to provide richer types in future versions of this
   specification (possibly more of which can be borrowed from json-
   schema.org).






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   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, model
   affordances that, when triggered, have more effect than just reading,
   updating, or observing Thing state, often resulting 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 multiple data parameters; these are modeled as input
   data and output data (using "sdfData" definitions, i.e., the same
   entries as for "sdfProperty" declarations).  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 "sdfPoperty";
   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.

   Actions may have (or lack) qualities of idempotency and side-effect
   safety.

   The current version of 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 can model
   affordances that inform about "happenings" associated with an
   instance of an Object; these may result in a signal being stored or
   emitted as a result.












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   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.

   The current version of 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 invoking the action, are expected to be part of the
   protocol binding.

2.2.5.  sdfData

   Definitions in "sdfData" groups 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.

   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" groups enables definition of
   models for complex devices that will use one or more "sdfObject"
   definitions.

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










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2.2.7.  sdfProduct

   "sdfThing" has a derived class "sdfProduct", which can be used to
   indicate a top level inventory item with a Stock-Keeping Unit (SKU)
   identifier and other particular metadata.  Structurally, there is no
   difference between definitions in either group; semantically, a
   definition in an "sdfProduct" group is intended to describe a class
   of complete Things.

3.  SDF structure

   SDF definitions are contained in SDF files.  One or more SDF files
   can work together to provide the definitions and declarations that
   are the payload of the SDF format.

   A SDF definition file contains a single JSON map (JSON object).  This
   object has three sections: the information block, the namespaces
   section, and the definitions section.

3.1.  Information block

   The information block contains generic meta data for the file itself
   and all included definitions.

   The keyword (map key) that defines an information block is "info".
   Its value is a JSON map in turn, with a set of entries that represent
   qualities that apply to the included definition.

   Qualities of the information block are shown in Table 1.

    +-----------+--------+----------+---------------------------------+
    | Quality   | Type   | Required | Description                     |
    +===========+========+==========+=================================+
    | title     | string | yes      | A short summary to be displayed |
    |           |        |          | in search results, etc.         |
    +-----------+--------+----------+---------------------------------+
    | version   | string | yes      | The incremental version of the  |
    |           |        |          | definition, format TBD          |
    +-----------+--------+----------+---------------------------------+
    | copyright | string | yes      | Link to text or embedded text   |
    |           |        |          | containing a copyright notice   |
    +-----------+--------+----------+---------------------------------+
    | license   | string | yes      | Link to text or embedded text   |
    |           |        |          | containing license terms        |
    +-----------+--------+----------+---------------------------------+

                Table 1: Qualities of the Information Block




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   While the format of the version string is marked as TBD, it is
   intended 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 an [RFC3339] "date-time" 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).

   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.  (For models to be handled by the One Data Model
   liaison group, this will typically be "BSD-3-Clause".)

3.2.  Namespaces section

   The namespaces section contains the namespace map and the
   defaultNamespace setting.

   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 definition
   file.

     +------------------+--------+----------+-----------------------+
     | Quality          | Type   | Required | Description           |
     +==================+========+==========+=======================+
     | namespace        | map    | no       | Defines short names   |
     |                  |        |          | mapped to namespace   |
     |                  |        |          | URIs, to be used as   |
     |                  |        |          | identifier prefixes   |
     +------------------+--------+----------+-----------------------+
     | defaultNamespace | string | no       | Identifies one of the |
     |                  |        |          | prefixes in the       |
     |                  |        |          | namespace map to be   |
     |                  |        |          | used as a default in  |
     |                  |        |          | resolving identifiers |
     +------------------+--------+----------+-----------------------+

                       Table 2: Namespaces Section

   The following example declares a set of namespaces and defines "cap"
   as the default namespace.





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

   If no defaultNamespace setting is given, the SDF definition file does
   not contribute to a global namespace.  As the defaultNamespace is set
   by giving 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 section

   The Definitions section contains one or more groups, each identified
   by a Class Name Keyword (there can only be one group per keyword; the
   actual grouping is just a shortcut and does not carry any specific
   semantics).  The value of each group is a JSON map (object), the keys
   of which serve for naming the individual definitions in this group,
   and the corresponding values provide the qualities (name-value pairs)
   for the individual definition.

   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 current definition block.

   A definition may in turn contain other definitions.  Each definition
   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 Object definition is given in Figure 4:

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

                    Figure 4: Example Object definition






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   This example defines an Object "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.

   Some of the definitions are also declarations: the definition of the
   entry "bar" in the property "foo" means that each instance of a "foo"
   can have zero or one instance of a "bar".  Entries within
   "sdfProperty", "sdfAction", and "sdfEvent", within "sdfObject"
   entries, are declarations.  Similarly, entries within an "sdfThing"
   describe instances of "sdfObject" (or nested "sdfThing") that form
   part of instances of the Thing.

4.  Names and namespaces

   SDF definition files may contribute to a global namespace, and may
   reference elements from that global namespace.  (An SDF definition
   file 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 versions 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.)

   The absolute URI of a global name should be a URI as per Section 3 of
   [RFC3986], with a scheme of "https" and a path ("hier-part" in
   [RFC3986]).  For the present version of this specification, the query
   part should not be used (it might be used in later versions).

   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
   definition file is constructed from a JSON pointer that selects the
   element defined for this name in the SDF definition file.

   The absolute URI part is a copy of the default namespace, i.e., the
   default namespace is always the target namespace for a name for which
   a definition is contributed.  When emphasizing that name definitions
   are contributed to the default namespace, we therefore also call it
   the "target namespace" of the SDF definition file.



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   E.g., 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

   Note the "#", which separates the base part from the fragment
   identifier part.

4.3.  Referencing global names

   A name reference takes the form of the production "curie" in
   [W3C.NOTE-curie-20101216] (note that this excludes the production
   "safe-curie"), but also limiting the IRIs involved in that production
   to URIs as per [RFC3986] and the prefixes to ASCII characters
   [RFC0020].

   A name that is contributed by the current SDF definition file can be
   referenced by a Same-Document Reference as per section 4.4 of
   [RFC3986].  As there is little point in referencing the entire SDF
   definition file, this will be a "#" followed by a JSON pointer.  This
   is the only kind of name reference that is possible in an SDF
   definition file that does not set a default namespace.

   Name references that point outside the current SDF definition file
   need to contain curie prefixes.  These then reference namespace
   declarations in the namespaces section.

   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"




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   Note that there is no way to provide a URI scheme name in a curie, so
   all references 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 or as
      sdfInput/OutputData etc.

4.4.  sdfRef

   In a JSON map establishing a definition, the keyword "sdfRef" is used
   to copy all of the qualities 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
   [I-D.handrews-json-schema-validation].)

   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.

4.5.  sdfRequired

   The value of "sdfRequired" is an array of name references, each
   pointing to one declaration the instantiation of which is declared
   mandatory.

4.5.1.  Optionality using the keyword "sdfRequired"

   The keyword "sdfRequired" is provided to apply a constraint that
   defines for which declarations corresponding data are mandatory in an
   instance conforming the current definition.

   The value of "sdfRequired" is an array of JSON pointers, each
   indicating one declaration that is mandatory to be represented.









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   The example in Figure 5 shows two required elements in the sdfObject
   definition for "temperatureWithAlarm", the sdfProperty
   "temperatureData", and the sdfEvent "overTemperatureEvent".  The
   example also shows the use of JSON pointer with "sdfRef" to use a
   pre-existing definition in this definition, for the "alarmType" data
   (sdfOutputData) produced by the sdfEvent "overTemperatureEvent".

   {
     "sdfObject": {
       "temperatureWithAlarm": {
         "sdfRequired": [
           "#/sdfObject/temperatureWithAlarm/sdfData/temperatureData",
           "#/sdfObject/temperatureWithAlarm/sdfEvent/overTemperatureEvent"
         ],
         "sdfData":{
           "temperatureData": {
             "type": "number"
           }
         },
         "sdfEvent": {
           "overTemperatureEvent": {
             "sdfOutputData": {
               "alarmType": {
                 "sdfRef": "cap:/sdfData/alarmTypes/quantityAlarms",
                 "const": "OverTemperatureAlarm"
               },
               "temperature": {
                 "sdfRef": "#/sdfObject/temperatureWithAlarm/sdfData/temperatureData"
               }
             }
           }
         }
       }
     }
   }

                        Figure 5: Using sdfRequired

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 label is required for an application and no label is
   given, the last part ("reference-token", Section 3 of [RFC6901]) of
   the JSON pointer to the definition can be used.





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    +-------------+--------------+-----------------------------------+
    | Quality     | Type         | Description                       |
    +=============+==============+===================================+
    | description | text         | long text (no constraints)        |
    +-------------+--------------+-----------------------------------+
    | label       | text         | short text (no constraints)       |
    +-------------+--------------+-----------------------------------+
    | $comment    | text         | source code comments only, no     |
    |             |              | semantics                         |
    +-------------+--------------+-----------------------------------+
    | sdfRef      | sdf-pointer  | (see Section 4.4)                 |
    +-------------+--------------+-----------------------------------+
    | sdfRequired | pointer-list | (see Section 4.5, applies to      |
    |             |              | qualities of properties, of data) |
    +-------------+--------------+-----------------------------------+

                        Table 3: Common Qualities

4.7.  Data Qualities

   Data qualities are used in "sdfData" and "sdfProperty" definitions.

   Table 4 lists data qualities borrowed from
   [I-D.handrews-json-schema-validation]; the intention is that these
   qualities retain their semantics from the versions of the json-
   schema.org proposal they were imported from.

   Table 5 lists data qualities defined specifically for the present
   specification.

   The term "allowed types" stands for primitive JSON types as well as
   homogeneous arrays of numbers, text, or Booleans.  (This list might
   be extended in a future version of SDF.)  An "allowed value" is a
   value allowed for one of these types.

   +----------------+---------------+--------------------------------------+
   | Quality        | Type          | Description                          |
   +================+===============+======================================+
   | type           | "number" /    | JSON data type                       |
   |                | "string" /    |                                      |
   |                | "boolean" /   |                                      |
   |                | "integer" /   |                                      |
   |                | "array"       |                                      |
   +----------------+---------------+--------------------------------------+
   | enum           | array of      | enumeration constraint               |
   |                |allowed values |                                      |
   +----------------+---------------+--------------------------------------+
   | const          | allowed value |specifies a constant value for a data |



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   |                |               | item or property                     |
   +----------------+---------------+--------------------------------------+
   | default        | allowed value | specifies the default value for      |
   |                |               | initialization                       |
   +----------------+---------------+--------------------------------------+
   | minimum        | number        | lower limit of value                 |
   +----------------+---------------+--------------------------------------+
   | maximum        | number        | upper limit of value                 |
   +----------------+---------------+--------------------------------------+
   |exclusiveMinimum| number or     | lower limit of value                 |
   |                | boolean (jso  |                                      |
   |                | draft 7/4)    |                                      |
   +----------------+---------------+--------------------------------------+
   |exclusiveMaximum| number or     | lower limit of value                 |
   |                | boolean (jso  |                                      |
   |                | draft 7/4)    |                                      |
   +----------------+---------------+--------------------------------------+
   | multipleOf     | number        | resolution of the number [NEEDED?]   |
   +----------------+---------------+--------------------------------------+
   | minLength      | integer       | shortest length string in octets     |
   +----------------+---------------+--------------------------------------+
   | maxLength      | integer       | longest length string in octets      |
   +----------------+---------------+--------------------------------------+
   | pattern        | string        | regular expression to constrain a    |
   |                |               | string pattern                       |
   +----------------+---------------+--------------------------------------+
   | format         | "date-time" / | JSON Schema formats as per           |
   |                |"date" / "time"|[I-D.handrews-json-schema-validation],|
   |                |/ "uri" / "uri-| Section 7.3                          |
   |                | reference" /  |                                      |
   |                | "uuid"        |                                      |
   +----------------+---------------+--------------------------------------+
   | minItems       | number        | Minimum number of items in array     |
   +----------------+---------------+--------------------------------------+
   | maxItems       | number        | Maximum number of items in array     |
   +----------------+---------------+--------------------------------------+
   | uniqueItems    | boolean       | if true, requires items to be all    |
   |                |               | different                            |
   +----------------+---------------+--------------------------------------+
   | items          | (subset of    | constraints on array items           |
   |                | common/data   |                                      |
   |                |qualities; see |                                      |
   |                | Appendix A    |                                      |
   +----------------+---------------+--------------------------------------+

     Table 4: Qualities of sdfProperty and sdfData borrowed from json-
                                 schema.org




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   +---------------+---------------+-------------------------+---------+
   | Quality       | Type          | Description             | Default |
   +===============+===============+=========================+=========+
   | (common)      |               | Section 4.6             |         |
   +---------------+---------------+-------------------------+---------+
   | units         | string        | SenML unit name as      | N/A     |
   |               |               | per [IANA.senml],       |         |
   |               |               | subregistry SenML       |         |
   |               |               | Units                   |         |
   +---------------+---------------+-------------------------+---------+
   | scaleMinimum  | number        | lower limit of          | N/A     |
   |               |               | value in units          |         |
   +---------------+---------------+-------------------------+---------+
   | scaleMaximum  | number        | upper limit of          | N/A     |
   |               |               | value in units          |         |
   +---------------+---------------+-------------------------+---------+
   | readable      | boolean       | Reads are allowed       | true    |
   +---------------+---------------+-------------------------+---------+
   | writable      | boolean       | Writes are allowed      | true    |
   +---------------+---------------+-------------------------+---------+
   | observable    | boolean       | flag to indicate        | true    |
   |               |               | asynchronous            |         |
   |               |               | notification is         |         |
   |               |               | available               |         |
   +---------------+---------------+-------------------------+---------+
   | 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                |         |
   +---------------+---------------+-------------------------+---------+
   | subtype       | "byte-string" | subtype                 | N/A     |
   |               | / "unix-time" | enumeration             |         |
   +---------------+---------------+-------------------------+---------+

         Table 5: SDF-defined Qualities of sdfProperty and sdfData

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.






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5.1.  sdfObject

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

   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 object              |
   +-------------+----------+------------------------------------------+
   | sdfAction   | action   | zero or more named action                |
   |             |          | definitions for this object              |
   +-------------+----------+------------------------------------------+
   | sdfEvent    | event    | zero or more named event                 |
   |             |          | definitions for this object              |
   +-------------+----------+------------------------------------------+
   | sdfData     | data     | zero or more named data                  |
   |             |          | type definitions that might              |
   |             |          | be used in the above                     |
   +-------------+----------+------------------------------------------+

                      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 common qualities
   and the data qualities, see Section 4.7.

5.3.  sdfAction

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




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   Actions are used to model commands and methods which are invoked.
   Actions have parameter data that are supplied upon invocation.

   The qualities of an Action definition include the common qualities,
   additional qualities are shown in Table 7.

     +----------------------+-------+--------------------------------+
     | Quality              | Type  | Description                    |
     +======================+=======+================================+
     | (common)             |       | Section 4.6                    |
     +----------------------+-------+--------------------------------+
     | sdfInputData         | array | Array of JSON Pointers to Data |
     |                      |       | items in the input data for an |
     |                      |       | Action                         |
     +----------------------+-------+--------------------------------+
     | sdfRequiredInputData | array | Array of JSON Pointers to      |
     |                      |       | mandatory Data items in the    |
     |                      |       | input data for an Action       |
     +----------------------+-------+--------------------------------+
     | sdfOutputData        | array | Array of JSON Pointers to Data |
     |                      |       | items in the Output data for   |
     |                      |       | an Action (mandatory items are |
     |                      |       | listed under sdfRequired)      |
     +----------------------+-------+--------------------------------+
     | sdfData              | data  | zero or more named data type   |
     |                      |       | definitions that might be used |
     |                      |       | in the above                   |
     +----------------------+-------+--------------------------------+

                      Table 7: Qualities of sdfAction

   "sdfInputData", as refined by "sdfRequiredInputData", define the
   input data of the action.  "sdfOutputData", as refined by
   "sdfRequired," (a quality defined in Table 3) define the output data
   of the action.

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 which are
   communicated upon the occurrence of the event.

   The qualities of sdfEvent include the common qualities, additional
   qualities are shown in Table 8.





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   +---------------+-------+------------------------------------------+
   | Quality       | Type  | Description                              |
   +===============+=======+==========================================+
   | (common)      |       | Section 4.6                              |
   +---------------+-------+------------------------------------------+
   | sdfOutputData | array | Array of JSON Pointers to Data items in  |
   |               |       | the Output data for an Action (mandatory |
   |               |       | items are listed under sdfRequired)      |
   +---------------+-------+------------------------------------------+
   | sdfData       | data  | zero or more named data type definitions |
   |               |       | that might be used in the above          |
   +---------------+-------+------------------------------------------+

                      Table 8: Qualities of sdfEvent

   "sdfOutputData", as refined by "sdfRequired" (a quality defined in
   Table 3), define the output data of the action.

5.5.  sdfData

   The sdfData keyword denotes a group of zero or more Data type
   definitions.

   An sdfData definition provides a semantic identifier for a data item
   and describes the constraints on the defined data item.

   sdfData is used for Action parameters, for Event output data, and for
   reusable constraints in Property definitions.

   The qualities of sdfData include the common qualities and the data
   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 Objects.

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

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




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

   *  The ability to reference items in one part of a complex definition
      from another part of the same definition, for example to summarize
      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 definition files that are present in 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.  There is expected to be an SDF namespace for
   common SDF definitions used in OneDM.

   The structure of a path in a namespace is defined by the JSON
   Pointers to the definitions in the files in that namespace.  For
   example, if there is a file defining an object "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
   (could be in the same file or another file) 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 re-use 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 which uses the defined qualities of some existing
   definition.  This pattern will use 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.  Optionally,
   new qualities may be added and values of optional qualities and
   quality values may be defined.

   ISSUE: Do we want to enable qualities from the source definition to
   be overridden in future versions?  The above only says "added".
   (Yes, we do want to enable overriding, but need to warn specifiers
   not to use this in a way that contradicts the referenced semantics.)





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   "sdfData":
     "length" : {
       "type": "number",
       "minimum": 0,
       "units": "m"
       "description": "There can be no negative lengths."
     }
   ...
     "cable-length" : {
       "sdfRef": "#/sdfData/length"
       "minimum": 0.05,
       "description": "Cables must be at least 5 cm."
     }

6.3.  sdfThing

   An sdfThing is a set of declarations and qualities that may be part
   of a more complex model.  For example, the object declarations that
   make up the definition of a single socket of an outlet strip could be
   encapsulated in an sdfThing, and the socket-thing itself could be
   used in a declaration in the sdfThing definition for the outlet
   strip.

   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.

   The qualities of sdfThing are shown in Table 9.

                   +-----------+--------+-------------+
                   | Quality   | Type   | Description |
                   +===========+========+=============+
                   | (common)  |        | Section 4.6 |
                   +-----------+--------+-------------+
                   | sdfThing  | thing  |             |
                   +-----------+--------+-------------+
                   | sdfObject | object |             |
                   +-----------+--------+-------------+

                      Table 9: Qualities of sdfThing
                              and sdfProduct








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6.4.  sdfProduct

   An sdfProduct provides the level of abstraction for representing a
   unique product or a profile for a standardized type of product, for
   example a "device type" definition with required minimum
   functionality.

   Products may be composed of Objects and Things at the high level, and
   may include their own definitions of Properties, Actions, and Events
   that can be used to extend or complete the included Object
   definitions.

   Product definitions may set optional defaults and constant values for
   specific use cases, for example units, range, and scale settings for
   properties, or available parameters for Actions.

   The qualities of sdfProduct are the same as for sdfThing and are
   shown in Table 9.

7.  References

7.1.  Normative References

   [I-D.handrews-json-schema-validation]
              Wright, A., Andrews, H., and B. Hutton, "JSON Schema
              Validation: A Vocabulary for Structural Validation of
              JSON", Work in Progress, Internet-Draft, draft-handrews-
              json-schema-validation-02, 17 September 2019,
              <http://www.ietf.org/internet-drafts/draft-handrews-json-
              schema-validation-02.txt>.

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

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

   [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>.

   [RFC3986]  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>.



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   [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>.

   [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>.

   [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>.

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

   [W3C.NOTE-curie-20101216]
              Birbeck, M. and S. McCarron, "CURIE Syntax 1.0", World
              Wide Web Consortium NOTE NOTE-curie-20101216, 16 December
              2010, <http://www.w3.org/TR/2010/NOTE-curie-20101216>.

7.2.  Informative References

   [I-D.irtf-t2trg-rest-iot]
              Keranen, A., Kovatsch, M., and K. Hartke, "RESTful Design
              for Internet of Things Systems", Work in Progress,
              Internet-Draft, draft-irtf-t2trg-rest-iot-06, 11 May 2020,
              <http://www.ietf.org/internet-drafts/draft-irtf-t2trg-
              rest-iot-06.txt>.

   [OCF]      "OCF Resource Type Specification",
              <https://openconnectivity.org/specs/
              OCF_Resource_Type_Specification.pdf>.

   [OMA]      "OMA LightweightM2M (LwM2M) Object and Resource Registry",
              <http://www.openmobilealliance.org/wp/omna/lwm2m/
              lwm2mregistry.html>.

   [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>.

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




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Appendix A.  Formal Syntax of SDF

   This appendix describes the syntax of SDF using CDDL [RFC8610].  Note
   that this appendix was derived from Ari Keranen's "alt-schema" and
   Michael Koster's "schema", with a view of covering the syntax that is
   currently in use at the One Data Model "playground" repository.

   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.

   start = sdf-syntax

   sdf-syntax = {
    info: sdfinfo                  ; don't *require* this in flexible syntax, though
    ? namespace: named<text>
    ? defaultNamespace: text
    ? sdfThing: named<thingqualities>       ; Thing is a composition of objects that work together in some way
    ? sdfProduct: named<productqualities>   ; Product is a composition of things and objects that can model a SKU-level instance of a product
    ? sdfObject: named<objectqualities>     ; Object is a set of Properties, Actions, and Events that together perform a particular function
    ? sdfProperty: named<propertyqualities> ; Property represents the state of an instance of an object
    ? sdfAction: named<actionqualities>     ; Action is a directive to invoke an application layer verb associated with an object
    ? sdfEvent: named<eventqualities>       ; Event represents an occurence of something associated with an object
    ? sdfData: named<dataqualities>         ; 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
    EXTENSION-POINT
   }

   sdfinfo = {
    title: text
    version: text
    copyright: text
    license: text
    EXTENSION-POINT
   }

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

   EXTENSION-POINT = ( * text => any ) ; only used in framework syntax

   sdf-pointer = text ; .regexp curie-regexp -- TO DO!
   pointer-list = [* sdf-pointer]  ; ISSUE: no point in having an empty list, no? but used for sdfRequired in odmobject-multiple_axis_joystick.sdf.json

   commonqualities = (



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    ? description: text            ; long text (no constraints)
    ? label: text                  ; short text (no constraints); default to key
    ? $comment: text               ; source code comments only, no semantics
    ? sdfRef: sdf-pointer
    ? sdfRequired: pointer-list    ; applies to qualities of properties, of data
   )

   ; for building hierarchy
   thingqualities = {
    commonqualities,
    ? sdfObject: named<objectqualities>
    ? sdfThing: named<thingqualities>
    EXTENSION-POINT
   }

   productqualities = thingqualities ; ISSUE: get rid of sdfProduct?

   ; for single objects
   objectqualities = {
    commonqualities,
    ? sdfProperty: named<propertyqualities>
    ? sdfAction: named<actionqualities>
    ? sdfEvent: named<eventqualities>
    ? sdfData: named<dataqualities>
    EXTENSION-POINT
   }

   propertyqualities = dataqualities ; the definitions in sdfData are declarations in sdfProperty

   actionqualities = {
    commonqualities,
    ? sdfInputData: pointer-list   ; sdfRequiredInputData applies here (a bit redundant)
    ? sdfRequiredInputData: pointer-list
    ? sdfOutputData: pointer-list  ; sdfRequired applies here
    ? sdfData: named<dataqualities>         ; zero or more named data type definitions that might be used in the above
    EXTENSION-POINT
   }

   eventqualities = {
    commonqualities
    ? sdfOutputData: pointer-list  ; sdfRequired applies here
    ? sdfData: named<dataqualities>         ; zero or more named data type definitions that might be used in the above
    EXTENSION-POINT
   }

   dataqualities = {               ; also propertyqualities
    commonqualities,
    jsonschema,



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    ? units: text
    ? scaleMinimum: number
    ? scaleMaximum: number
    ? observable: bool
    ? readable: bool
    ? writable: bool
    ? nullable: bool
    ? subtype: "byte-string" / "unix-time"
              / text                       ; EXTENSION-POINT
    ? contentFormat: text
    EXTENSION-POINT
   }

   allowed-types = number / text / bool / null
                 / [* number] / [* text] / [* bool]
                 / any                     ; EXTENSION-POINT

   jsonschema = (
    ? type: "number" / "string" / "boolean" / "integer" / "array" ; / "object"
              / text                       ; EXTENSION-POINT
    ? enum: [+ allowed-types]                                              ; should validate against type
    ? const: allowed-types
    ? default: allowed-types
    ; number/integer constraints
    ? minimum: number
    ? maximum: number
    ? exclusiveMinimum: bool / number      ; jso draft 4/7
    ? exclusiveMaximum: bool / number      ; jso draft 4/7
    ? multipleOf: number                   ; ISSUE: Do we need this?
    ; text string constraints
    ? minLength: number
    ? maxLength: number
    ? pattern: text                ; regexp
    ? format: "date-time" / "date" / "time"
              / "uri" / "uri-reference" / "uuid"
              / text                       ; EXTENSION-POINT
              ; expand on demand
    ; array constraints
    ? minItems: number
    ? maxItems: number
    ? uniqueItems: bool
    ? items: { ;;; ultimately, this will be mostly recursive, but, for now
               ;;; let's find out what we actually need
        ? sdfRef: sdf-pointer          ; import limited to the subset that we allow here...
        ? description: text            ; long text (no constraints)
        ? $comment: text               ; source code comments only, no semantics
        ; commonqualities, ; -- ISSUE: should leave this out for non-complex data types, but need the above three
        ? type: "number" / "string" / "boolean" / "integer" ; no "array" / "object"



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              / text                       ; EXTENSION-POINT
        ; jso subset
        ? minimum: number
        ? maximum: number
        ? enum: [+ any]
        ? format: text
        ? minLength: number
        ? maxLength: number
        EXTENSION-POINT
      }
   )

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

   This appendix describes the syntax of SDF defined in Appendix A, but
   using a version of the description techniques advertised on json-
   schema.org [I-D.handrews-json-schema-validation].

   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",
   +  "title": "sdf-framework.cddl",
      "$schema": "http://json-schema.org/draft-07/schema#",
      "$ref": "#/definitions/sdf-syntax",
      "definitions": {
        "sdf-syntax": {
          "type": "object",
          "required": [
            "info"
          ],
          "properties": {
            "info": {
              "$ref": "#/definitions/sdfinfo"
            },
            "namespace": {
              "type": "object",
              "additionalProperties": {
                "type": "string"
              }
            },
            "defaultNamespace": {
              "type": "string"



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            },
            "sdfThing": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/thingqualities"
              }
            },
            "sdfProduct": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/productqualities"
              }
            },
            "sdfObject": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/objectqualities"
              }
            },
            "sdfProperty": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/propertyqualities"
              }
            },
            "sdfAction": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/actionqualities"
              }
            },
            "sdfEvent": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/eventqualities"
              }
            },
            "sdfData": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/dataqualities"
              }
            }
          },
   -      "additionalProperties": false
   +      "additionalProperties": {
   +      }
        },



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        "sdfinfo": {
          "type": "object",
          "required": [
            "title",
            "version",
            "copyright",
            "license"
          ],
          "properties": {
            "title": {
              "type": "string"
            },
            "version": {
              "type": "string"
            },
            "copyright": {
              "type": "string"
            },
            "license": {
              "type": "string"
            }
          },
   -      "additionalProperties": false
   +      "additionalProperties": {
   +      }
   +    },
   +    "EXTENSION-POINT": {
   +      "type": "object",
   +      "additionalProperties": {
   +      }
        },
        "thingqualities": {
          "type": "object",
          "properties": {
            "sdfObject": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/objectqualities"
              }
            },
            "sdfThing": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/thingqualities"
              }
            },
            "description": {
              "type": "string"



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            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            }
          },
   -      "additionalProperties": false
   +      "additionalProperties": {
   +      }
        },
        "commonqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            }
          },
          "additionalProperties": false
        },
        "sdf-pointer": {
          "type": "string"
        },
        "pointer-list": {
          "type": "array",
          "items": {
            "$ref": "#/definitions/sdf-pointer"
          }
        },



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        "objectqualities": {
          "type": "object",
          "properties": {
            "sdfProperty": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/propertyqualities"
              }
            },
            "sdfAction": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/actionqualities"
              }
            },
            "sdfEvent": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/eventqualities"
              }
            },
            "sdfData": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/dataqualities"
              }
            },
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            }
          },
   -      "additionalProperties": false
   +      "additionalProperties": {
   +      }
        },
        "propertyqualities": {



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          "$ref": "#/definitions/dataqualities"
        },
        "dataqualities": {
          "type": "object",
          "properties": {
            "units": {
              "type": "string"
            },
            "scaleMinimum": {
              "type": "number"
            },
            "scaleMaximum": {
              "type": "number"
            },
            "observable": {
              "type": "boolean"
            },
            "readable": {
              "type": "boolean"
            },
            "writable": {
              "type": "boolean"
            },
            "nullable": {
              "type": "boolean"
            },
            "subtype": {
   -          "type": "string",
   -          "enum": [
   -            "byte-string",
   -            "unix-time"
   +          "anyOf": [
   +            {
   +              "type": "string",
   +              "const": "byte-string"
   +            },
   +            {
   +              "type": "string",
   +              "const": "unix-time"
   +            },
   +            {
   +              "type": "string"
   +            }
              ]
            },
            "contentFormat": {
              "type": "string"
            },



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            "type": {
   -          "type": "string",
   -          "enum": [
   -            "number",
   -            "string",
   -            "boolean",
   -            "integer",
   -            "array"
   +          "anyOf": [
   +            {
   +              "type": "string",
   +              "const": "number"
   +            },
   +            {
   +              "type": "string",
   +              "const": "string"
   +            },
   +            {
   +              "type": "string",
   +              "const": "boolean"
   +            },
   +            {
   +              "type": "string",
   +              "const": "integer"
   +            },
   +            {
   +              "type": "string",
   +              "const": "array"
   +            },
   +            {
   +              "type": "string"
   +            }
              ]
            },
            "enum": {
              "type": "array",
              "items": {
                "$ref": "#/definitions/allowed-types"
              },
              "minItems": 1
            },
            "const": {
              "$ref": "#/definitions/allowed-types"
            },
            "default": {
              "$ref": "#/definitions/allowed-types"
            },
            "minimum": {



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              "type": "number"
            },
            "maximum": {
              "type": "number"
            },
            "exclusiveMinimum": {
              "anyOf": [
                {
                  "type": "boolean"
                },
                {
                  "type": "number"
                }
              ]
            },
            "exclusiveMaximum": {
              "anyOf": [
                {
                  "type": "boolean"
                },
                {
                  "type": "number"
                }
              ]
            },
            "multipleOf": {
              "type": "number"
            },
            "minLength": {
              "type": "number"
            },
            "maxLength": {
              "type": "number"
            },
            "pattern": {
              "type": "string"
            },
            "format": {
   -          "type": "string",
   -          "enum": [
   -            "date-time",
   -            "date",
   -            "time",
   -            "uri",
   -            "uri-reference",
   -            "uuid"
   +          "anyOf": [
   +            {



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   +              "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"
   +            }
              ]
            },
            "minItems": {
              "type": "number"
            },
            "maxItems": {
              "type": "number"
            },
            "uniqueItems": {
              "type": "boolean"
            },
            "items": {
              "type": "object",
              "properties": {
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "description": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"



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                },
                "type": {
   -              "type": "string",
   -              "enum": [
   -                "number",
   -                "string",
   -                "boolean",
   -                "integer"
   +              "anyOf": [
   +                {
   +                  "type": "string",
   +                  "const": "number"
   +                },
   +                {
   +                  "type": "string",
   +                  "const": "string"
   +                },
   +                {
   +                  "type": "string",
   +                  "const": "boolean"
   +                },
   +                {
   +                  "type": "string",
   +                  "const": "integer"
   +                },
   +                {
   +                  "type": "string"
   +                }
                  ]
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "enum": {
                  "type": "array",
                  "minItems": 1
                },
                "format": {
                  "type": "string"
                },
                "minLength": {
                  "type": "number"
                },
                "maxLength": {
                  "type": "number"



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                }
              },
   -          "additionalProperties": false
   +          "additionalProperties": {
   +          }
            },
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            }
          },
   -      "additionalProperties": false
   +      "additionalProperties": {
   +      }
        },
        "jsonschema": {
          "type": "object",
          "properties": {
            "type": {
   -          "type": "string",
   -          "enum": [
   -            "number",
   -            "string",
   -            "boolean",
   -            "integer",
   -            "array"
   +          "anyOf": [
   +            {
   +              "type": "string",
   +              "const": "number"
   +            },
   +            {
   +              "type": "string",
   +              "const": "string"
   +            },
   +            {
   +              "type": "string",



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   +              "const": "boolean"
   +            },
   +            {
   +              "type": "string",
   +              "const": "integer"
   +            },
   +            {
   +              "type": "string",
   +              "const": "array"
   +            },
   +            {
   +              "type": "string"
   +            }
              ]
            },
            "enum": {
              "type": "array",
              "items": {
                "$ref": "#/definitions/allowed-types"
              },
              "minItems": 1
            },
            "const": {
              "$ref": "#/definitions/allowed-types"
            },
            "default": {
              "$ref": "#/definitions/allowed-types"
            },
            "minimum": {
              "type": "number"
            },
            "maximum": {
              "type": "number"
            },
            "exclusiveMinimum": {
              "anyOf": [
                {
                  "type": "boolean"
                },
                {
                  "type": "number"
                }
              ]
            },
            "exclusiveMaximum": {
              "anyOf": [
                {
                  "type": "boolean"



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                },
                {
                  "type": "number"
                }
              ]
            },
            "multipleOf": {
              "type": "number"
            },
            "minLength": {
              "type": "number"
            },
            "maxLength": {
              "type": "number"
            },
            "pattern": {
              "type": "string"
            },
            "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"
   +            },



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   +            {
   +              "type": "string",
   +              "const": "uuid"
   +            },
   +            {
   +              "type": "string"
   +            }
              ]
            },
            "minItems": {
              "type": "number"
            },
            "maxItems": {
              "type": "number"
            },
            "uniqueItems": {
              "type": "boolean"
            },
            "items": {
              "type": "object",
              "properties": {
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "description": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "type": {
   -              "type": "string",
   -              "enum": [
   -                "number",
   -                "string",
   -                "boolean",
   -                "integer"
   +              "anyOf": [
   +                {
   +                  "type": "string",
   +                  "const": "number"
   +                },
   +                {
   +                  "type": "string",
   +                  "const": "string"
   +                },
   +                {
   +                  "type": "string",



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   +                  "const": "boolean"
   +                },
   +                {
   +                  "type": "string",
   +                  "const": "integer"
   +                },
   +                {
   +                  "type": "string"
   +                }
                  ]
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "enum": {
                  "type": "array",
                  "minItems": 1
                },
                "format": {
                  "type": "string"
                },
                "minLength": {
                  "type": "number"
                },
                "maxLength": {
                  "type": "number"
                }
              },
   -          "additionalProperties": false
   +          "additionalProperties": {
   +          }
            }
          },
          "additionalProperties": false
        },
        "allowed-types": {
          "anyOf": [
            {
              "type": "number"
            },
            {
              "type": "string"
            },
            {
              "type": "boolean"



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            },
            {
              "type": "null"
            },
            {
              "type": "array",
              "items": {
                "type": "number"
              }
            },
            {
              "type": "array",
              "items": {
                "type": "string"
              }
            },
            {
              "type": "array",
              "items": {
                "type": "boolean"
              }
   +        },
   +        {
            }
          ]
        },
        "actionqualities": {
          "type": "object",
          "properties": {
            "sdfInputData": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfRequiredInputData": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfOutputData": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfData": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/dataqualities"
              }
            },
            "description": {
              "type": "string"
            },
            "label": {



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              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            }
          },
   -      "additionalProperties": false
   +      "additionalProperties": {
   +      }
        },
        "eventqualities": {
          "type": "object",
          "properties": {
            "sdfOutputData": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfData": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/dataqualities"
              }
            },
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            }
          },
   -      "additionalProperties": false
   +      "additionalProperties": {
   +      }
        },



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        "productqualities": {
          "$ref": "#/definitions/thingqualities"
        }
      }
    }

Acknowledgements

   This draft is based on "sdf.md" and "sdf-schema.json" in the old one-
   data-model "language" repository, as well as Ari Keranen's "alt-
   schema" from the Ericsson Research "ipso-odm" repository (which is
   now under subdirectory "sdflint" in the one-data model "tools"
   repository).

Contributors

   Ari Keränen
   Ericsson
   FI-02420 Jorvas
   Finland

   Email: ari.keranen@ericsson.com


   Wouter van der Beek
   Cisco Systems
   Eastpoint Business Park
   Alfie Byrne Road
   Dublin 3
   Ireland

   Email: wovander@cisco.com


Authors' Addresses

   Michael Koster (editor)
   SmartThings
   665 Clyde Avenue
   Mountain View,  94043
   United States of America

   Phone: +1-707-502-5136
   Email: Michael.Koster@smartthings.com







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   Carsten Bormann (editor)
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.org











































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