OWL-S
To have an Ontology is not sufficient, indeed a "interface" is missing
between the Web Service and the Ontology. That's why W3C submitted
OWL-S
(Previously known as DAML-S) to exploit the Semantic informations contained
into the Ontolgy and so allowing to semantically "enrich" Web Services.
OWL-S provides a set of "entities" to
describe the properties and capacities of Web Services.
OWL-S was thought to make easier the tasks related to Web Services
like their automated discovery, their execution, their composition
or their interoperability.
OWL-S is composed of four entites where the Service class provides
the entry point for the description of a Web Services.
There is one and only one instanciation of the Service class per Web Service.
- The ServiceProfile give us informations about services proposed by the Web Services. It will allow to software agents to reach all the information necessary to evaluate if the Web Service suit to their needs.
-
The ServiceModel knows how the service works. It can be used in
four different manners :
- To make a deeper analysis of the Web Service.
- To compose service descriptions from several services to do a specific task.
- to coordinate the different participants activities taking part to the service execution.
- To supervise service execution.
-
The ServiceGrounding defines the access modalities to the service.
Typically, the ServiceGrounding will specify a communication protocol,
the format of messages and others details related to the technical use of service.
Furthermore, the ServiceGrounding is used to define for each abstract type, a clear specification on the manner to exchange data of this type.
- A service must be describe by a maximun of one ServiceModel.
- A service must have one and only one ServiceGrounding.
Like the prototype of dynamic discovery of a Web Services workflow will be based on a intermediation, the ServiceProfile will be mainly solicited. It will give us the possibility to access to all the needed informations for the intermedation algorithm.
Semantic Enrichment of a Web Service
The production of OWL-S files is made in two phases.
First, I used a tool developed by MINDSWAP
(Maryland Information and Network Dynamics Lab Semantic Web Agents Project) named
WSDL2OWL which from a WSDL creates a OWL-S File (based of course on
WSDL's data).
This automatic creation will only bring you fifty percent of the needed informations
for a interesting use of OWL-S.
Indeed, if the ServiceProcess and the ServiceGrounding
are relatively quite well filled, the ServiceProfile must to be
defined completely. But that's logical : the semantic nature of informations
are unfortunately not easily deductible starting from the WSDL.