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Semantic Web Services 177
annotation. The tool uses WSDL for description but offers also the possibility to export them
to OWL-S.
6.2.1 WSDL-S
WSDL-S [1] is one of the possible formal descriptions of services. It defines the meaning
of the inputs, outputs, preconditions and effects of the operations described in a service
interface.
WSDL-S does not define a language that spans across the different levels of the web
service stack, rather it is limited to WSDL simplifying the task of providing semantic representation
of services. WSDL-S makes a low commitment to OWL and it provides a general
annotation mechanism which could be used in conjunction with any meta language including
UML. This allows to annotate web services with concepts from multiple ontologies from
different sources.
6.2.2 OWL-S
OWL-S (also known as DAML-S) [63] presents an OWL [54] ontology of services motivated
by the need of providing knowledge about a service. Figure 6-8 shows the core of the OWL-S.
The base is the Service class which has three main properties:
– presents, which range is a ServiceProfile: class defining what does the service require
from the consumers and what it offers them.
– describedBy, which range is a ServiceModel: class defining how the service works.
– supports, which range is a ServiceGrounding: class defining how is the service used.
Resource
provides
Service
presents
supports
ServiceProfile
What the
service
does
ServiceModel
describedBy
ServiceGrounding
How to
access it
How it
works
Figure 6-8. OWL-S core (retrieved from [63]).
Each instance of a Service class present a descendant class of a ServiceProfile, bedescribedBy
a descendant class of ServiceModel, and support a descendant class of ServiceGrounding.