Introduction to WSMO - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 56

a means to describe Web services that provide access (searching, buying,
etc.) to services. WSMO is designed as a means to describe the former and
not to replace the functionality of the latter.

5.2 Top-Level Elements of WSMO

Following the key aspects identified in the Web Service Modeling Framework,
WSMO identifies four top-level elements as the main concepts: ontologies,
services, goals, and mediators (Fig. 5.1). These have to be described in order
to describe Semantic Web services:

Goals

Ontologies Web Services

Mediators

Fig. 5.1. WSMO core elements

As introduced in Chapter 3, ontologies provide the terminology used and
are the key element for the success of Semantic Web services. WSMO de-
scribes an epistemology of ontologies, i.e. the conceptual building blocks such
as concepts and relations.
The actual Web services are computational entities that provide some
value in a certain domain. Web service descriptions consist of their capability,
their interfaces, and their orchestration-the internal workings of the service.
Goals describe aspects related to user desires with respect to the requested
functionality; again, ontologies can be used in order to define the domain
terminology used to describe the relevant aspects of goals. Goals model the
user's view of the Web service usage process and therefore are a separate
top-level entity in WSMO.
Finally, Mediators describe elements that handle interoperability problems
between different elements, for example two different ontologies or services.
We envision mediators as a core concept for resolving incompatibilities on the
data, process, and protocol levels, i.e. they will be used in order to resolve
mismatches between different terminologies (data level), to communicate be-
tween services (protocol level), and to combine Web services and goals (process
level).
These top-level elements of WSMO are discussed and defined in Chapter

6.