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6
The Concepts of WSMO
In the case of complex systems, one cannot make sense of the constituent
parts without first understanding the whole. Parts can only make sense in the
context of a greater whole.
Our hope is that the previous chapter has provided the reader with some
sort of conceptual understanding of WSMO (although only a general overview
at best), at least enough to be able to understand the contention that WSMO
does not fall prey to the problems of the family of complex systems. Neverthe-
less, the present chapter will follow the “grandfatherly” advice of complexity
theory just the same, attempting to “make sense of the constituent parts”.
In this chapter, we describe further the core elements of WSMO: we present
ontologies in Section 6.1, Web services in Section 6.2, goals in Section 6.3, and
mediators in Section 6.4. Section 6.5 presents an informal discussion of the
nonfunctional properties that are part of the WSMO conceptual model.
6.1 Ontologies
Ontologies were introduced in Chapter 3 and although there are currently
several standardizations efforts for ontology languages [60, 32, 64], none of
them have the desired expressivity and computational properties that are
required to describe Web services at a su
cient level of granularity. In the
following, we shall define an epistemological model which is general enough to
intuitively capture existing languages. In the next chapter of this topic we shall
present a concrete language specifically designed to express this metamodel.
Now we present the conceptual model and introduce the elements that
constitute an ontology using the MOF notation, defining the class “ontology”
with its attributes. The following listing specifies the building blocks for an
ontology. Note that all attributes are optional. Thus an ontology can have
multiple instances of all elements; however, this is not a requirement.
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