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180 Selected Studies on Software and Information Systems
WSMO corresponds to the meta-model layer of the architecture. A WSMO description
of a concrete web service is related to the model layer. The concrete web service is placed in
the information layer.
MOF
metametamodel
M3 Layer
metamodel
M2 Layer
WSMO
model
information
M1 Layer
M0 Layer
WSMO descriptions
Concrete Web Services, Domains
and Data to be described
Figure 6-10. The relation between WSMO and MOF (retrieved from [70]).
WSMO identifies four top-level elements which define the semantics of the web service:
– Ontologies: provide a vocabulary to describe different aspects of web services.
– Web services: represent computational entities able to provide access to services. Web
service is in WSMO described from three points of view: non-functional, functional
and behavioral. The functionality is described by one and only one capability. The
behavior may be described by multiple interfaces.
– Goals: describe aspects related to user desires with respect to the requested functionality.
It is characterized in dual way. The goal’s description includes the requested
capability and requested interface.
– Mediators: describe elements that handle interoperability problems between different
WSMO elements. They describe elements aiming at overcoming structural, semantic
and conceptual mismatches between them.
To express the WSMO model, WSMO uses the WSML language [30].
6.3 Semantic Web Service Coordination
Semantic web service coordination aims at satisfying the users’ goals using Semantic web
service discovery, composition and execution [45]. Figure 6-11 presents an overview of the
utilization of web service composition by a user. The user can be a human, an agent or an
application invoking the service. The first step of this process is gathering the information
about the goal. For this goal, taking the input data and considering preconditions, the
composition process starts including web services discovery. The discovery is responsible
for searching for the web services in the available registries. During composition the domain
knowledge is exploited to enhance the used methods. The domain knowledge is stored
in ontologies linked to the Semantic web services’ descriptions. When the composition is
constructed, it is executed. This results in output data and effects in which the user is
interested in.