Semantic Web Service Usage Tasks in WSMO - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 124

the same - apart from different concrete literals - so that the same Web
services must be usable for resolving both goals. This allows the definition
of beneficial algorithmic procedures for avoiding or reducing the need for
expensive reasoning operations in functional Web service discovery. We
refer to [121] for details of this technique.
9.3.2 Mediation Components
The second dimension of the WSMO mediation technology relates to the
logical components that utilize the mediation techniques presented above in
order to resolve mismatches. As a consequence of the dynamic and evolving
nature of the Semantic Web, an essential design principle for a comprehensive
mediation architecture is modularity , i.e. delegation of mediation to distinct
components in order to enable reusability of mediation facilities [41].
The WSMO metamodel defines four types of mediators that appear to
be applicable within the Web service usage process. The mediator type is
indicated by a prefix denoting the types of the source and target components.
Each mediator type applies those mediation techniques which are required for
resolving the heterogeneities that can possibly occur between the connected
components. Figure 9.8 gives an overview of the WSMO mediator typology
with respect to the mediation techniques used.
Fig. 9.8. WSMO mediator topology
OO mediators provide the data-level mediation component. The source
elements are ontologies or other OO mediators, while the target can be any
top-level WSMO element. The only mediation technique used is data-level me-
diation. OO mediators provide a general mediation component for ontology-
based applications; the other mediator types are specific to Web services.
GG mediators connect WSMO goals, i.e. both the source and the target are
goals. The mediation techniques used are data mediation via OO mediators
and functional level mediation on the basis of ∆ -relations that precisely define
the logical relationship between the source and target goals.