]> Ericsson

petri.laari@ericsson.com

ART ASDF Working Group Internet-Draft 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.

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. 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) . 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. 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 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.

Terminology This specification uses the terminology specified in , 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 when, and only when, they appear in all capitals, as shown here.

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.

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 , we can use the following namespace definition: { "namespace": { "saref": "https://saref.etsi.org/saref4bldg/v1.1.2/" } }

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.

Quality	Type	Required	Description
relType	string/IRI?	no	What kind of relationship 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

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.

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" } } } ...

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.)

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.

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.

property Object with key-value pairs that describe additional properties for this relationship. Details TBD.

writable Is the information of the relation writable, i.e., can be changed. Default: false.

Example relation description In the following example, we have a definition for first-object which located next to second-object: "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" } } } }

SDF DTDL mapping This section (to be removed) shows mapping between SDF and DTDL qualities for relations.

Quality (SDF)	Quality (DTDL)	Description	Required
sdfRelation	@type	In DTDL, this is "Relationship", this is the objects sdfRelation entity	yes
"name-of-relation"	name	In SDF, this is the entity name	yes
relType	@id	DTDL: The ID of the relationship description	no
writable	writable	Boolean, is this relation writable or not	no
target	target	An Interface ID, in SDF the target definition	no
$comment	comment	This is for model authors in DTDL	no
description	description	DTDL: localizable description for display	no
	displayName	DTDL: localizable name for display	no
property	properties	A set of Properties that define relationship-specific state	no
maxItems	maxMultiplicity	max nof target instances	no
minItems	minMultiplicity	min nof target instances	no

Security Considerations TODO Security

IANA Considerations This document has no IANA actions.

References Normative References PassiveLogic Universität Bremen TZI 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. 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. Tools convert this format to database formats and other serializations as needed. // A JSON format representation of SDF 1.0 was defined in version // (-00) of this document; version (-05) was designated as an // _implementation draft_, labeled SDF 1.1, at the IETF110 meeting of // the ASDF WG (2021-03-11). The present version (-12) collects // smaller changes up to 2022-06-30. It also removes deprecated // elements from SDF 1.0. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Universität Bremen TZI This document defines and registers an sdfType "link" for the Semantic Definition Format (SDF) for Data and Interactions of Things (draft-ietf-asdf-sdf-12.txt).

Acknowledgments The author wants to thank Ari Keranen, Mikko Saarisalo, and Christer Holmberg for their feedback and comments.