Internet DRAFT - draft-laari-asdf-relations
draft-laari-asdf-relations
ASDF Working Group P. Laari
Internet-Draft Ericsson
Intended status: Standards Track 13 September 2023
Expires: 16 March 2024
Extended relation information for Semantic Definition Format (SDF)
draft-laari-asdf-relations-02
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 in class
level descriptions. This specification does not consider instance-
specific information.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 16 March 2024.
Copyright Notice
Copyright (c) 2023 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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 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. label . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Example relation description with sdfType links . . . . . 6
4. DTDL - SDF conversion . . . . . . . . . . . . . . . . . . . . 7
4.1. DTDL specific conversion . . . . . . . . . . . . . . . . 9
4.1.1. DTDL @type and DTDL name . . . . . . . . . . . . . . 9
4.1.2. DTDL @id . . . . . . . . . . . . . . . . . . . . . . 9
4.1.3. DTDL comment . . . . . . . . . . . . . . . . . . . . 9
4.1.4. DTDL description . . . . . . . . . . . . . . . . . . 9
4.1.5. DTDL displayName . . . . . . . . . . . . . . . . . . 9
4.1.6. max and minMultiplicity . . . . . . . . . . . . . . . 10
4.1.7. DTDL properties . . . . . . . . . . . . . . . . . . . 10
4.1.8. DTDL target . . . . . . . . . . . . . . . . . . . . . 10
4.1.9. DTDL writable . . . . . . . . . . . . . . . . . . . . 10
4.1.10. SDF Relation type . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11
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.
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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.
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 than plain parent-child relations. 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".
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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.
3. SDF Relation Extension
This section defines a new SDF Class Name Keyword, sdfRelation, that
can be used to describe complex relations. The relationship
definitions are on class-level, i.e., the sdfRelation keyword does
not describe instance specific information about the relation, but
describes how different models and definitions relate to each other.
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 |
| | IRI? | | relationship these |
| | | | definitions have |
+-------------+---------+----------+--------------------------------+
| target | string | no | Target model for the |
| | | | relation |
+-------------+---------+----------+--------------------------------+
| description | string | no | Description of the |
| | | | relationship |
+-------------+---------+----------+--------------------------------+
| label | string | no | Short text describing |
| | | | the relationship |
+-------------+---------+----------+--------------------------------+
| property | object | no | Additional properties |
| | | | for this relation / |
| | | | this is inherited from |
| | | | DTDL, not valid for SDF |
+-------------+---------+----------+--------------------------------+
| $comment | string | no | Additional comments for |
| | | | implementors |
+-------------+---------+----------+--------------------------------+
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. For example, this can
be #/sdfObject/room, when the target object room 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?)
In addition to SDF definitions, the target can be also a reference to
another ontology. For example, a temperature sensor SDF definition
can be augmented with information that a SAREF definition of a
TemperatureSensor has similar semantics as this SDF definition.
"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. label
Short text describing the relationship, similar to label quality in
other SDF definitions.
3.3. Example relation description with sdfType links
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": {
"adjacent-node": {
"type": "object",
"sdfType": "link"
}
},
"sdfRelation": {
"next-to": {
"description": "This object is adjacent to the second
object",
"relType": "exont:next-to",
"target": "#/sdfObject/second-object"
}
}
},
"second-object": {
"description": "Example object, next to the first object",
"sdfProperty": {
"adjacent-node": {
"type": "object",
"sdfType": "link"
}
...
},
"sdfRelation": {
"next-to": {
"relType": "exont:next-to",
"target": "#/sdfObject/first-object"
}
}
}
}
4. DTDL - SDF conversion
This section (to be removed) discusses the mapping between SDF and
DTDL qualities.
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+=================+=============+=======================+==========+
| Quality (DTDL) | Quality | Description | Required |
| | (SDF) | | in DTDL |
+=================+=============+=======================+==========+
| @type | sdfRelation | DTDL Interface | yes |
| | | (Relationship), maps | |
| | | to sdfRelation in SDF | |
+-----------------+-------------+-----------------------+----------+
| @id | - | DTDL: The ID of the | no |
| | | relationship | |
| | | description | |
+-----------------+-------------+-----------------------+----------+
| comment | $comment | A comment for model | no |
| | | authors | |
+-----------------+-------------+-----------------------+----------+
| description | description | DTDL: localizable | no |
| | | description for | |
| | | display | |
+-----------------+-------------+-----------------------+----------+
| displayName | label | DTDL: localizable | no |
| | | name for display | |
+-----------------+-------------+-----------------------+----------+
| maxMultiplicity | - | max multiplicity for | no |
| | | the target, maps to | |
| | | maxItems in SDF | |
| | | instance | |
+-----------------+-------------+-----------------------+----------+
| minMultiplicity | - | min multiplicity for | no |
| | | the target (must be | |
| | | zero), maps to | |
| | | minItems in SDF | |
| | | instance | |
+-----------------+-------------+-----------------------+----------+
| name | "name of | The programming name | yes |
| | relation" | of the element | |
+-----------------+-------------+-----------------------+----------+
| properties | to | A set of Properties | no |
| | sdfProperty | that define | |
| | | Relationship-specific | |
| | | state | |
+-----------------+-------------+-----------------------+----------+
| target | target | An interface | no |
| | | identifier of the | |
| | | target (or "any" if | |
| | | not specified) | |
+-----------------+-------------+-----------------------+----------+
| writable | - | A boolean value that | no |
| | | indicates whether the | |
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| | | Relationship is | |
| | | writable or not, maps | |
| | | to SDF instance | |
| | | "writable" | |
+-----------------+-------------+-----------------------+----------+
Table 2
4.1. DTDL specific conversion
4.1.1. DTDL @type and DTDL name
This defines the sdfRelation itself and the name is the name of the
sdfRelation entry, i.e. @type Relationship and name converts to:
...
"sdfRelation": {
"name-from-DTDL": {
...
}
}
4.1.2. DTDL @id
In the example DTDL files, this is never present. This is the
identifier for the relationship, no further definition in the
specification. In DTDL this value is given automatically if it does
not exist in the DTDL model file.
4.1.3. DTDL comment
This can be converted to $comment and it is a comment for the
implementors.
4.1.4. DTDL description
This maps directly to the SDF "description".
4.1.5. DTDL displayName
This converts to the "label" field in SDF.
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4.1.6. max and minMultiplicity
These define how many instances of the relationship can exist of the
target type. The sdfRelation is purely a class-level definition, but
sdfType "link" defines the actual instance specific information.
Thus, these fields map to maxItems and minItems in the corresponding
sdfType "link" definition.
4.1.7. DTDL properties
Relationship definition in DTDL may contain additional properties
(key-value pairs) that describe additional properties for this
relationship. This can be converted into sdfProperty in the same
object as where the sdfRelation definion is.
4.1.8. DTDL target
In DTDL this is the Interface of the target, in SDF this maps to the
target object of this relation.
4.1.9. DTDL writable
The relationship itself is not defined to be writable, but this field
maps to the SDF instance and to the corresponding sdfType "link"
definition.
4.1.10. SDF Relation type
In SDF, the relType is giving the type of the relationship, e.g.
isControlledBy. However, in DTDL, this is not directly described in
the DTDL file.
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>.
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[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., Bormann, C., and A. Keränen, "Semantic
Definition Format (SDF) for Data and Interactions of
Things", Work in Progress, Internet-Draft, draft-ietf-
asdf-sdf-15, 4 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-asdf-
sdf-15>.
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-01, 3 June
2023, <https://datatracker.ietf.org/doc/html/draft-
bormann-asdf-sdftype-link-01>.
[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.
Author's Address
Petri Laari
Ericsson
Email: petri.laari@ericsson.com
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