Extended relation information for Semantic Definition Format (SDF)
draft-laari-asdf-relations-01
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Petri Laari | ||
| Last updated | 2022-12-12 | ||
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draft-laari-asdf-relations-01
ASDF Working Group P. Laari
Internet-Draft Ericsson
Intended status: Standards Track 12 December 2022
Expires: 15 June 2023
Extended relation information for Semantic Definition Format (SDF)
draft-laari-asdf-relations-01
Abstract
The Semantic Definition Format (SDF) base specification defines set
of basic information elements that can be used for describing a large
share of the existing data models from different ecosystems. While
these data models are typically very simple, such as basic sensors
definitions, more complex models, and in particular bigger systems,
benefit from ability to describe additional information on how
different definitions relate to each other. This document specifies
an extension to SDF for describing complex relationships and
additional information about them.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 15 June 2023.
Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SDF Relation Extension . . . . . . . . . . . . . . . . . . . 4
3.1. Namespaces . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Qualities of sdfRelation . . . . . . . . . . . . . . . . 4
3.2.1. relType . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. target . . . . . . . . . . . . . . . . . . . . . . . 6
3.2.3. description . . . . . . . . . . . . . . . . . . . . . 6
3.2.4. maxItems . . . . . . . . . . . . . . . . . . . . . . 6
3.2.5. minItems . . . . . . . . . . . . . . . . . . . . . . 7
3.2.6. property . . . . . . . . . . . . . . . . . . . . . . 7
3.2.7. writable . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Example relation description . . . . . . . . . . . . . . 7
4. SDF DTDL mapping . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The Semantic Definition Format (SDF) [SDF] is a format for domain
experts to use in the creation and maintenance of data and
interaction models in the Internet of Things. The SDF specification
defines a generic data model that can be used as a meta model when
converting between other data models, such as IPSO Smart Objects or
Digital Twins Definition Language (DTDL) [DTDL]. SDF model defines a
set of affordances, describing the interfaces for the Object. These
can be mapped to corresponding affordances in other data models.
The base specification defines ways to represent parent-child
relations between two definitions. However, sometimes there is a
need to describe also more complex relations to support arbitrary
connections between definitions and also referring to definitions
outside of the SDF models. These could be, for example, defining
possible location of a device inside a room, how a device is
controlled by another device, or physical topology between devices.
This enables defining more complex systems using SDF models.
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The basic parent-child relations between SDF Objects and Things can
be defined by including a definition of a child in the definition of
the parent. This covers a large share of simple data models
defining, e.g., simple sensors, or more complex devices containing a
set of sensors. On the other hand, SDF can be used also to describe
even more complex entities, such as buildings with rooms and other
related objects inside a building. When we extend the SDF usage, the
simple parent-child relation is often not enough, but more complex
relations may be needed to describe the connections between the
definitions. These relations can be for example physical (e.g., an
object is inside another object), functional (e.g., an object can
control another object), or semantic (e.g., an object is similar to a
term defined in another ontology).
This document extends the base SDF specification by adding a new
keyword to describe also other relations between physical or logical
objects. This new keyword is needed to describe, without loss of
information, models from ecosystems that are using complex relation
information in their definitions.
This extension enables describing relations from SDF models to
various (SDF or other) definitions. For a link data type for
affordances, e.g., for a link property that can be accesses and
modified during runtime, the "sdfType for links" extension
[I-D.bormann-asdf-sdftype-link] can be used instead.
NOTE: This extension is now defined based on the Relationships
feature in the DTDL specification. There may be other kind of
definitions for relationships in other data models that must be taken
into account and this specification may need to be extended to cover
also those requirements.
2. Terminology
This specification uses the terminology specified in [SDF], in
particular "Class Name Keyword", "Object", and "Affordance".
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.
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3. SDF Relation Extension
In this section we define a new SDF Class Name Keyword, sdfRelation,
that can be used to describe complex relations. The definitions are
on class-level, i.e., the sdfRelation keyword does not give any
instance specific information about the relation, but defines the
potential relations between definitions.
3.1. Namespaces
The SDF namespace block can be used to provide CURIE prefixes for
external ontologies for use with sdfRelation extension. For example,
in case of SAREF (Smart Applications REFerence ontology) ontology
extension for buildings [saref4bldg], we can use the following
namespace definition:
{
"namespace": {
"saref": "https://saref.etsi.org/saref4bldg/v1.1.2/"
}
}
3.2. Qualities of sdfRelation
In this section, the qualities of the sdfRelation are defined. These
qualities are used to define the potential type of the connection
between the definitions and to which definition the connection can be
made.
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+=============+=========+==========+=============================+
| Quality | Type | Required | Description |
+=============+=========+==========+=============================+
| relType | string/ | no | What kind of relationship |
| | IRI? | | these definitions have |
+-------------+---------+----------+-----------------------------+
| target | string | no | Target definition for the |
| | | | relation |
+-------------+---------+----------+-----------------------------+
| description | string | no | Description of the |
| | | | relationship |
+-------------+---------+----------+-----------------------------+
| maxItems | integer | no | Maximum number of instances |
| | | | of the target types |
+-------------+---------+----------+-----------------------------+
| minItems | integer | no | Minimum number of instances |
| | | | of the target types |
+-------------+---------+----------+-----------------------------+
| property | object | no | Additional properties for |
| | | | this relation |
+-------------+---------+----------+-----------------------------+
| writable | boolean | no | Is the target writable or |
| | | | not |
+-------------+---------+----------+-----------------------------+
Table 1
3.2.1. relType
The relType quality describes what kind of relationship this
definition has to the target definition. This can use different
ontologies, such as SAREF from ETSI. The used ontology MUST be
defined in the namespace block to give a short name for the ontology
IRI.
For example the "relType" field could define the relationship to be
saref:isControlledByDevice, when the SAREF ontology is used with
CURIE prefix "saref" defined in the namespace block for the full IRI
https://saref.etsi.org/saref4bldg/v1.1.2/. The defined purpose for
the relation is a functional relationship between the two
definitions.
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3.2.2. target
The "target" field defines to which definition or ontology term this
definition with sdfRelation has a relation to. This can be e.g.
#/sdfObject/room, when the target object is defined in the same SDF
model. This may also be left undefined, and in that case the
relation may be any other object (Note: This is from DTDL (check),
does it make sense in SDF context?)
The target does not have to be another SDF object, but it can be also
a reference to another ontology. For example, we may have a
Temperature sensor, which relation to SAREF temperature sensor is
defined and it is the same as this one.
"namespace": {
"exont": "https://example.com/relationOntology",
"saref": "https://saref.etsi.org/core/v3.1.1/"
},
sdfObject: {
"temperature": {
"description": "Example temperature object",
"sdfProperty": {
...
},
"sdfRelation": {
"sameAs": {
"relType": "exont:same-as",
"target": "saref:TemperatureSensor"
}
}
}
...
3.2.3. description
The description of the relationship. For SDF version 1.1, the
description is a string. (For future SDF versions this description
can be localizable, allowing different languages in the description.)
3.2.4. maxItems
Maximum number of instances of the target definition that can be
related to this definition. If not specified, the number of
instances is not limited.
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3.2.5. minItems
The minimum number of instances of the target definition that must
exist for this definition. If defined, this value MUST be between
zero and maxItems. Default: 0.
3.2.6. property
Object with key-value pairs that describe additional properties for
this relationship. Details TBD.
3.2.7. writable
Is the information of the relation writable, i.e., can be changed.
Default: false.
3.3. Example relation description
In the following example, we have a definition for first-object which
located next to second-object:
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"namespace": {
"exont": "https://example.com/relationOntology"
},
sdfObject: {
"first-object": {
"description": "Example object",
"sdfProperty": {
...
},
"sdfRelation": {
"next": {
"relType": "exont:next-to",
"target": "#/sdfObject/second-object"
}
}
},
"second-object": {
"description": "Example object, next to the first object",
"sdfProperty": {
...
},
"sdfRelation": {
"next": {
"relType": "exont:next-to",
"target": "#/sdfObject/first-object"
}
}
}
}
4. SDF DTDL mapping
This section (to be removed) shows mapping between SDF and DTDL
qualities for relations.
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+==================+===============+=====================+========+
|Quality (SDF) |Quality (DTDL) |Description |Required|
+==================+===============+=====================+========+
|sdfRelation |@type |In DTDL, this is |yes |
| | |"Relationship", this | |
| | |is the objects | |
| | |sdfRelation entity | |
+------------------+---------------+---------------------+--------+
|"name-of-relation"|name |In SDF, this is the |yes |
| | |entity name | |
+------------------+---------------+---------------------+--------+
|relType |@id |DTDL: The ID of the |no |
| | |relationship | |
| | |description | |
+------------------+---------------+---------------------+--------+
|writable |writable |Boolean, is this |no |
| | |relation writable or | |
| | |not | |
+------------------+---------------+---------------------+--------+
|target |target |An Interface ID, in |no |
| | |SDF the target | |
| | |definition | |
+------------------+---------------+---------------------+--------+
|$comment |comment |This is for model |no |
| | |authors in DTDL | |
+------------------+---------------+---------------------+--------+
|description |description |DTDL: localizable |no |
| | |description for | |
| | |display | |
+------------------+---------------+---------------------+--------+
| |displayName |DTDL: localizable |no |
| | |name for display | |
+------------------+---------------+---------------------+--------+
|property |properties |A set of Properties |no |
| | |that define | |
| | |relationship-specific| |
| | |state | |
+------------------+---------------+---------------------+--------+
|maxItems |maxMultiplicity|max nof target |no |
| | |instances | |
+------------------+---------------+---------------------+--------+
|minItems |minMultiplicity|min nof target |no |
| | |instances | |
+------------------+---------------+---------------------+--------+
Table 2
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5. Security Considerations
TODO Security
6. IANA Considerations
This document has no IANA actions.
7. References
7.1. Normative References
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[SDF] Koster, M. and C. Bormann, "Semantic Definition Format
(SDF) for Data and Interactions of Things", Work in
Progress, Internet-Draft, draft-ietf-asdf-sdf-12, 30 June
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
asdf-sdf-12>.
7.2. Informative References
[DTDL] "Digital Twins Definition Language (DTDL) v2", 10 February
2022, <https://github.com/Azure/opendigitaltwins-
dtdl/blob/master/DTDL/v2/dtdlv2.md>.
[I-D.bormann-asdf-sdftype-link]
Bormann, C., "An sdfType for Links", Work in Progress,
Internet-Draft, draft-bormann-asdf-sdftype-link-00, 1
December 2022, <https://datatracker.ietf.org/doc/html/
draft-bormann-asdf-sdftype-link-00>.
[saref4bldg]
Poveda-Villalón, M. and R. Garcia-Castro, "SAREF extension
for building", 5 June 2020,
<https://saref.etsi.org/saref4bldg>.
Acknowledgments
The author wants to thank Ari Keranen, Mikko Saarisalo, and Christer
Holmberg for their feedback and comments.
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Author's Address
Petri Laari
Ericsson
Email: petri.laari@ericsson.com
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