WoT Reasoning

The aim of this project was to demonstrate how to add reasoning capabilities to Web of Things application platforms. Currently, it can infer properties so as to discover devices that have not been formally declared in a WoT Runtime, thanks to ad hoc reasoning rules.

This project is based on the following technologies:

• node-red and its upper-layer iot-schema-node-red as WoT application programming environment,
• Thingweb Directory as support for WoT device descriptions in W3C Thing Description vocabulary, and
• GraphDB as both persistence layer for device semantic descriptions and semantic reasoner.

Getting started

node-red :

• Installation: sudo npm install -g --unsafe-perm node-red
• Launching: node-red

GraphDB

• Installation (8.10.1 recommended; requires Java 8): https://www.ontotext.com/products/graphdb/graphdb-free/
• Launching:
  1. cd graphdb-free-8.10.1/bin
  2. ./graphdb -d

GraphDB Web interface will be accessible at http://localhost:7200

ThingWeb Directory

• Installation (requires a particular version of WoT TD): git clone https://github.com/thingweb/thingweb-directory/tree/4641f260190805034ed11c11b0591280fca06d1b
• Launching:
  1. set environment variables to match thingweb and GraphDB:
     export THINGWEB_SPARQL_QUERY_ENDPOINT=http://localhost:7200/repositories/<your_repository_name>
export THINGWEB_SPARQL_UPDATE_ENDPOINT=http://localhost:7200/repositories/<your_repository_name>/statements
  2. cd thingweb-directory/directory-app
  3. gradle run

iotschema-node-red

• Installation:
  1. git clone https://github.com/iot-schema-collab/iotschema-node-red
  2. Go into node-red local folder: Linux: $ cd ~/.node-red Windows (Powershell): PS C:\Users\{username}\AppData\Roaming\npm\node_modules\node-red
  3. $ npm i -g recursive-install
  4. $ npm-recursive-install --rootDir={YOUR_OWN_PATH}/iotschema-node-red
• Launching: iotschema-node-red devices and capabilities will be available on node-red interface.

Repository contents

• wot-reasoning-example.json is a basic example of device description (to add in node-red) that contains the definition of a KelvinTemperatureDevice.
• builtin_owl2-rl_modified.pie is the ruleset to add when creating a new RDF repository in GraphDB. It contains:
  • the definition of OWL2RL semantics,
  • the definition, as a set of rules, of a second device: kelvin_to_celsius, which performs temperature unit conversion.
  • some specific inference rules (at the end of the file) defining a property chain to be used with the example below,

Note: it is of course possible to define the kelvin_to_celsius convertor in the TD json file instead of the GraphDB ruleset.

Using the example

Based on the definitions of a KelvinTemperatureDevice and a kelvin_to_celsius converter, this example infers a CelsiusTemperatureDevice which is queriable in SPARQL.

node-red side

• Open wot-reasoning-example.json in node-red and on the thing-directory tab, choose the Use Remote TD Server option then type localhost:8080 (i.e. the adress used for thingweb)
• Store the TD
• The recipe will be automatically redirected to GraphDB

GraphDB side

The GraphDB SPARQL endpoint should expose both the KelvinTemperatureSensor node and an implicit node called CelsiusTemperatureSensor inferred by the reasoner (if activated in the project settings) using the provided ruleset.

You should be able to query both nodes of type "iot:TemperatureSensor" using:

SELECT * WHERE {
    ?s iot:capability "iot:TemperatureSensor".  
    ?s ?p ?o.
}

This query shows that the reasoner has created a KelvinTemperatureSensor (i.e. a device that produces temperature observation results in Kelvin).

Note: the rule that generates this new device is an ad hoc rule. It still needs to be expressed using an OWL property chain axiom to be generalized and more useful.

Troubleshooting

• EACCESS problem when starting node-red -> $ sudo npm config set unsafe-perm=true

Credits

This project was realized during Nicolas Condomitti's first year master degree internship and funded by the computer science department of Université Claude Bernard Lyon 1.