Thing Description

From Web of Things Interest Group

Task force on Thing Description

This task force is chartered to address following aspects:

  • Clarify and define what the TDL can be used for
  • Clarify and define what aspects of a Thing can be described
  • Agreement on the three building elements:
    • What is a suitable data model underlying TDL
    • How would a vocabulary used in thing descriptions look like
    • What is an appropriate syntax / serialization format of TDL which is feasible for the Things (may be synchronized with the AP task force)

Work in progress

Currently discussed in the meetings

  • existing semantic techniques that are feasible for Things
  • data model

First Findings

Following findings are based on the presentations and discussions during the web meetings:

IETF CoRE Link Format

  • good starting point to capture what kind of resources the REST-based server provides
  • “rt” attribute can be used to add/link some ‘semantics’ (e.g., as a tag or a link to an ontology)
  • However, there is a need of a common understanding of following aspects:
    • meaning of a resource (e.g., ‘measuring temperature in Celsius in room 123’)
    • meaning of the data payload in terms of data types and data structures (check SenML? or XML Schema?)
  • Alternative to “rt” attribute: standardize a fix resource to request the complete Thing description
    • e.g., define '/meta' as resource that serves the full semantic description of the Thing

W3C RDF data model

  • Standardized and Universal Graph representation
  • Exist different kinds of serialization formats:
    • JSON and JSON-LD
    • XML
    • N3
    • Turtle
    • EXI (for resource constrained devices)
  • Available tools (e.g., for search, reasoning etc.)
    • Relevant for the resource discovery
  • Stream-able and can be used for semantic stream processing (see OpenIoT project)

W3C Semantic Sensor Network (SSN) Ontology

  • Describes sensors in terms of capabilities, measurement processes, observations and deployments;
  • The scope of the SSN ontology and its related use cases:
    • Data discovery and linking;
    • Device discovery and selection;
    • Provenance and diagnosis, and
    • Device operation, tasking and programming;
  • The SSN ontology:
    • is compatible with the OGC standards, and extensible with other semantic models;
    • may contribute to the TD vocabulary;
    • may serve for describing Things (when Things are sensors):
      • Events (e.g., stimuli, observations);
      • Properties (e.g., capabilities, conditions, ranges);
    • does not need to be wholly reused, e.g., use only observations or only sensors etc.


  • method of transporting Linked Date using JSON
  • JSON-LD covers RDF
    • serializiation varaint for RDF-based data
  • save spaces by the @context defination (comparable to prefix / namespaces usage in XML)

W3C/OGC Spatial Data on the Web working Group (SDWWG)

  • SDWWG is working on best practices for spatial data encoding, relation vocabularies, identity, geometry and APIs.
  • Planned standardization work:
    • OWL-time standard - ontology for the Gregorian calendar plus temporal relationships. Based on Allen’s interval calculus.
    • Semantic Sensor Networks (SSN) ontology - used widely in environmental sensing and Internet of Things.
  • Working Working Use Cases
  • The work from SDWWG (e.g., SSN, OWL-time) can be used as input for vocabularies and schemas of Thing Descriptions.

Sensor Markup Language (SenML)

  • What is SenML
    • SenML draft defines new media types for carrying simple sensor information in a protocol such as HTTP or CoAP.
    • It provides a structured and uniform mechanism to represent simple sensor measurement and device parameters.
    • Device parameters including name, id, type, unit, timestamp, version...
    • Software implementation using JSON or XML or EXI
  • Motivation
    • Constrained devices could easily encode a sensor measurement into the media type (application/senml+json).
    • M2M server parsing the data could relatively efficiently collect a large number of sensor measurements.
  • Data Model
    • The data is structured as a single object (with attributes) that contains an array of entries.
    • Each entry is an object that has attributes such as a unique identifier for the sensor, the time the measurement was made, and the current value.
    • Serializations of the data model are defined for JSON, XML and EXI.

IPSO Smart Object

  • based on LWM2M Object Model
  • reusable Object IDs and Resource IDs
  • is transport protocol and encoding data format independent
  • basic objects represent sensors and actuators
  • resources are defined by an object ID, object instance ID, and resource ID
    • e.g., 3303/0/5700
  • objects can be extended with additional properties / resources

RDF serializiation with EXI

  • RDF data use mainly string based values (especially for subjects and predicates)
  • EXI has an efficient encoding approach to handle strings and removes redundancy
    • relevant standardized serialization candidate for interacting with very constrained devices (e.g., microcontrollers)
  • a generic RDF EXI coder can be used for arbitrary RDF data or
  • an application specific RDF EXI coder can be used for known RDF data structures (e.g., knwon from an ontology)
  • hybrid approach (generic + specific RDF EXI coder) is also possible

Wot-TD Tech Landscape

Wot-TD Tech Landscape surveys existing technologies relevant to Thing Description.


It will start out with weekly calls and relax the schedule to bi-weekly calls when in operation.

The next call is scheduled for the 1th of July@ 1:00 CEST

Calls are using webex and in parallel the IRC channel #wot-td on


Web meeting minutes from 25th November 2015

Web meeting minutes from 11th November 2015, Slides

Web meeting minutes from 14th October 2015

Web meeting minutes from 16th September 2015

Web meeting minutes from 2nd September 2015

Web meeting minutes from 19th August 2015

Web meeting minutes from 12th August 2015

Web meeting minutes from 22nd July 2015

Web meeting minutes from 8th July 2015

Web meeting minutes from 1th July 2015

Web meeting minutes from 24th June 2015

Web meeting minutes from 17th June 2015

Web meeting minutes from 9th June 2015

Web meeting minutes from 3nd June 2015

Web meeting minutes from 27th May 2015

Web meeting minutes from 19th May 2015

Web meeting minutes from 13th May 2015