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WSMO reuses WSDL, the choreography model needs to be tied to the WSDL
model of operations.
In WSMO, choreography is modeled as an abstract state machine (Chap-
ter 6), where the states are described with an ontology, and the client is
(abstractly) allowed to read and write instances of certain concepts that are
marked as “in”, “out”, or “shared”, the latter meaning both “in” and “out”.
The state transition rules model the reactions to incoming data and the cre-
ation of outgoing data.
With this choreography model, WSMO is not limited to the message ex-
change view of Web services (see [39] (Triple Spaces) for an alternative). The
purpose of grounding is to give the client all the necessary networking details
so that it can successfully communicate with the service. When a client follows
the WSMO choreography state machine, it knows from the activated transi-
tion rules that some particular data can be sent to the service. The grounding
now binds this data to a WSDL operation request, and if the operation has a
response message, then the client knows that it can expect specific data back.
When creating the grounding, the designer takes into account all the “in”,
“out”, and “shared” concepts (since they are manipulated by the transition
rules), and correlates “in” and “shared” concepts with input messages, and
“out” and “shared” concepts with output messages.
WSMO is based on ontological models of Web services. These formal,
logic-based models describe those aspects of Web services that are necessary
for automating tasks such as service discovery, negotiation, composition, and
invocation. On the other hand, the IT industry deploys Web services with
only limited description capabilities, su cient when Web services are mostly
used, composed, and deployed manually. The industry standard for Web ser-
vice description is WSDL, a language that views Web service interfaces as
collections of operations, combined with XML Schema, a validation-oriented
language for describing XML data structures.
We have indicated how WSMO grounding information should be specified.
Data grounding is the main part of the grounding of Semantic Web services,
as there are several different approaches to one complex problem. The current
frameworks for Semantic Web services take various approaches: WSMO has
initially decided to use an approach that uses an intermediate XML Schema
ad hoc ontology. Together with the abstract ontology-mapping language pre-
sented above and the existing tool support, this provides the most e cient
means in our settings for achieving the task.
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