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188 Selected Studies on Software and Information Systems
A language GWorkflowDL for Grid workflow description and execution environment GWES
were developed.
Before this, the composition must be transformed into a form the interpreter works with.
The web service execution process can interleave with the planning. Based on this, we divide
the approaches to static and dynamic. Static means that during the planning no service is
executed. Dynamic approaches execute some services to examine the state of the world or
the availability of data.
One solution for web service execution is offered by WSMX 6 [26]. It provides an environment
for discovery, selection, mediation, invocation, and interoperation of web services.
WSMX is based on the conceptual model provided by WSMO. The main components of
WSMX are:
– Core component: central part of WSMX which coordinates all other components.
– Resource manager: manages the repositories of WSMO entities (web services, goals,
ontologies, and mediators) and other data.
– Service discovery: locates the web services that fulfill the user’s requirements.
– Service selection: selection of the best or optimal Semantic web service from the list of
those satisfying matching service.
– Data and process mediator: takes care about mediation when two entities are not able to
communicate or interact.
– Communication manager: supports communication between service requestor and
provider.
– Choreography engine: makes sure that the requestor’s and provider’s communication
patterns match.
– Web service modeling toolkit: supports the creation and deployment of tools for Semantic
web services for the developers.
– Reasoner: provides reasoning for the validation of composite services and checking if
it is executable in a given context.
WSMX presents a complex solution for all web service execution related concerns, however
not fully implemented at this time. Another instrument for web service execution is offered
by BPEL4WS 7 [4]. It is of the leading notation describing executable web service compositions.
The processes – workflows described in BPEL4WS can be executed with engines
working with this language. One of the existing, available implementations are BPWS4J 8
6 Web Service Execution Environment, http://www.w3.org/Submission/WSMX/
7 Business Process Execution Language for Web Services,
http://www.ibm.com/developerworks/library/specification/ws-bpel/
8 http://www.alphaworks.ibm.com/tech/bpws4j/