Web Services - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 46

Fig. 4.3. The GlobalWeather service viewed in an UDDI browser
location specifies the physical location of the service endpoint, however one
might also interpret it as the “scope” of the service. A human can easily de-
duce from the interface name GlobalWeather that this is not the case, but
for a software program interpreting the description, this is less obvious.
The description of published services also contains a link to a WSDL file
and, specifically, also to concrete interfaces (port types). Using this link, UDDI
provides a machine-processable access to the interface description of an service
and therefore, theoretically, also provides the possibility of automatic invoca-
tion of services. However we face the problem that both WSDL and UDDI
offer a mainly syntactic description.
4.3.4 Related WS-* Standards
A series of related standards and recommendations complete the technologies
that are nowadays commonly referred to as “Web services”. The components
described so far allow only the description of interactions that follow a simple
in/out process. However, typical business processes are more complex and
require descriptions of more complex interaction patterns.
The Business Process Execution Language for Web Services (BPEL4WS)
[4] allows one to describe such processes on the basis of services described
using WSDL. BPEL is an XML-based language for describing an executable
process over a series of Web service operations. This allows one to aggregate
atomic service operations into a more meaningful service component.
Note that WSDL, in principle, already allows one to group a set of related
operations together in a description; however, it provides no means to describe
any restriction on the possible sequences that those operations can be invoked
in. BPEL4WS can describe such concrete sequences, for example to first invoke
first a login operation, followed by subsequent search and buy operations.