Semantic Web Service Usage Tasks in WSMO - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 116

Discovery Based on Rich Semantic Descriptions
When they are a part of WSMO or another rich model description frameworks
such as OWL-S [87] or SWSF [9], functional descriptions of Web services are
syntactic expressions in some specification language using the precondition/-
postcondition style of description. This description specifies the possible state
transitions that are caused by service invocations. The logical formulas are
constructed from terms in an ontology, in a way in which the axiomatization
of these terms can be kept general (unspecific) and need not be repeated for
each service description.
Each description captures specific requirements for Web services and can
be used to constrain the set of all Web services to some subset that is relevant
to a particular context. At this level of abstraction, the descriptions describe
constraints on the valid prestates and resulting poststates. In contrast to the
previous level of abstraction, we are now able to describe relations between
such states; for example the balance of a bank account supplied as input may
be decreased by a certain amount.
9.2.3 Matching Goals and Web Services
The general approach is to look for certain types of logical relationships be-
tween the semantic capability descriptions of Web services and requests (i.e.
goals). If such a relationship holds, a Web service is considered to be usable
for resolving the client's goal. On the basis of several preceding studies on
semantic matchmaking [84, 106], we have identified five matchmaking notions
for functional discovery as shown in Fig. 9.4. The important characteristic of
these notions is that each one denotes a different logical relationship that must
hold true when considering whether a Web service is suitable for achieving a
given goal. For instance, an Exact Match holds if and only if each possible
ontology instance that can satisfy the Web service also satisfies the goal, and
there exists no possible ontology instance that satisfies only the goal or the
Web service. In contrast, an Intersection Match holds if there exists one pos-
sible instance that can satisfy both the goal and the Web service. Hence, in
order to precisely express client objectives with respect to discovery, WSMO
goals carry an additional non functional property typeOfMatch ,denotingthe
matchmaking notion to be applied.
Several prototypical realizations of semantically enabled discovery already
exist: [84] and [49] apply description logic reasoners, the approach in [71] is
based on frame- and transaction logic, and [123] uses a FOL theorem prover as
the technical platform for semantically enabled discovery. However, all these
approaches are restricted to the specific reasoning support provided by the
tools used. Hence, it is expected that these approaches will converge towards
an integrated discovery framework for Semantic Web services that provides
appropriate reasoning facilities.