ST 2005 Note #5 - Semantic Web Services
Web Service proponents know that the web has only grown so effectively because it allows individuals to establish their own web sites, date repositories, models, APIs etc. W3C standards are really substrates that allow individual expressions to be integrated at some level.
A Web Service world where every service in a subject area uses the same data model is unrealistic and does not reflect experience of the web to date. Web Service proponents need to find mechanisms to map between web services' different models of their domain.
UDDI is a current standard for service discovery. However, to query a UDDI registry the requestor must submit a query in the implicit ontology of the UDDI. What is actually required is the ability for a service provider to describe the capabilities of the service in one or more defined ontologies. A service requester should be able to search for a service using capabilities defined in one or more ontologies. Providing the discovery service has mappings between these ontologies then it will be able to provide matches to searches that may otherwise have returned no results.
Describing a web service using an ontology will not only aid searching but it will also aid use. For a requestor to use a service without additional coding it will need the service to specify the ontology for the terms used in the WSDL. In addition, a requester needs to understand pre and post-conditions for a service and the effects of a process or service. For example, if ordering a book from Amazon it would be helpful if a service requester could determine if an order would result in a book being dispatched or whether other process steps are needed. In the Semantic Web Services world OWL-S is attempting to provide some aspects of this functionality. A service can describe itself using OWL-S and document:
With these facilities, OWL-S is providing foundations for semantic discovery, automated web service composition and the ability for a requester to determine what the inputs and outputs mean. Further information can be found in this paper.
A Web Service world where every service in a subject area uses the same data model is unrealistic and does not reflect experience of the web to date. Web Service proponents need to find mechanisms to map between web services' different models of their domain.
UDDI is a current standard for service discovery. However, to query a UDDI registry the requestor must submit a query in the implicit ontology of the UDDI. What is actually required is the ability for a service provider to describe the capabilities of the service in one or more defined ontologies. A service requester should be able to search for a service using capabilities defined in one or more ontologies. Providing the discovery service has mappings between these ontologies then it will be able to provide matches to searches that may otherwise have returned no results.
Describing a web service using an ontology will not only aid searching but it will also aid use. For a requestor to use a service without additional coding it will need the service to specify the ontology for the terms used in the WSDL. In addition, a requester needs to understand pre and post-conditions for a service and the effects of a process or service. For example, if ordering a book from Amazon it would be helpful if a service requester could determine if an order would result in a book being dispatched or whether other process steps are needed. In the Semantic Web Services world OWL-S is attempting to provide some aspects of this functionality. A service can describe itself using OWL-S and document:
- Pre and post-conditions.
- Effects of operations.
- The semantics of the terms used in the WSDL.
- Capabilities of the service.
With these facilities, OWL-S is providing foundations for semantic discovery, automated web service composition and the ability for a requester to determine what the inputs and outputs mean. Further information can be found in this paper.
posted by Andy S at 8:19 AM
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