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
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
- 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.
- Presented at meeting 10 June 2015) File:SDWWG Kerry Taylor June2015.pdf
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
- 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.
- Further reading
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 irc.w3.org