Tools - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 145

Fig. 10.8. WSMX components

Service-oriented architectures typically consist of a set of services and a
coordinator that combines the services and puts them to use. Talking about
SOAs in the context of WSMX can sometimes be misleading since WSMX is
an SOA and at the same time it is the coordinator of another, larger SOA.
The WSMX differentiates between two types of services: application services
(such as discovery, choreography, and data and process mediation) and the
base service layer (e.g. storage). Application services are mandatory for en-
abling the infrastructure to deliver its functionality as defined by its execution
semantics. User services are exposed by information systems external to the
WSMX infrastructure, but they are still coordinated using WSMX platform
services. The WSMX recommendation defines the scope of particular plat-
form services in terms of their functionality, whereas it remains silent about
the scope and functionality of user services. Some of the components of WSMX
are the following:

• Discovery. The discovery component of WSMX is responsible for finding

Semantic Web service descriptions given a user's semantically described
goal. This component operates over all of the Web service descriptions
stored in WSMX's resource manager.

• Adoption. It is not feasible to presume that a Web service will be de-

scribed in an exhaustive manner. Considering the Amazon book service,
for instance, it would not be possible for Amazon to update the semantic
description every time a new book was made available or a price changed.
The adoption component of WSMX is responsible for communicating with
each of the discovered services, obtaining the additional information re-
quired on the basis of the interfaces provided by the service, and selecting
which of the discovered services is most suited to the user's requirements.
The user's goal can contain preference information that can be used by
the selection component to select between the various services on the basis
of their nonfunctional properties. These nonfunctional properties include
availability, reliability, scalability, and financial considerations.