Tools - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 146

• Composition. Part of a service interface describes how the service makes

use of other services to achieve its functionality. Composition and chore-
ography are related concepts but distinct from each other. The composi-
tion component is responsible for making use of other services in order to
achieve its functionality. It is the WSMX implementation of the strategies
discussed in Section 9.4.

• Choreography. The choreography part of a service interface describes the

behavior of the service from a client's point of view. Any user of a Web ser-
vice, automated or otherwise, is a client of that service. The choreography
engine is responsible for using the choreography descriptions of both the
service requester and the provider to drive the conversation between them.
It is the responsibility of the choreography engine to maintain the state of
a conversation and to take the correct action when that state is updated.
For example, updating of the state of a choreography instance may occur
as the result of a message received from a service provider. The consequent
action, as described in the choreography instance, could be to forward the
message unchanged to the service requester. The choreography engine in
the WSMX architecture has three main responsibilities: (1) evaluating the
transition rules defined in the choreography interface, (2) determining the
legal instances for the last choreography step, and (3) managing invocation
requests to and from the communication manager.

• Data mediation. The data mediation component of WSMX is responsible

for performing instance transformation when the ontologies used by the
goal are different from those used by the Web service. Data mediation may
occur at many different points in the execution semantics. Data mediation
in WSMX is a semiautomatic process, in which a domain expert must first
create the mappings between the two ontologies. This manual step occurs
in an o ine mode. Once these mappings have been created and registered
with WSMX, the data mediation component can automatically mediate
between these two ontologies in real time.

• Process mediation. The process mediation component is used to resolve

heterogeneity issues between the public processes of the requester and
the provider. For example, the requester may expect the user name and
password to be sent together, whereas the provider may expect them sep-
arately. The WSMX process mediation component provides an automatic
mechanism for resolving these process mismatches.

This is only a subset of the components present in the WSMX architecture.
Other, more low-level components include a resource manager for storing and
retrieving data; a communication manager for receiving requests from the
user and communicating with Web services; and the WSMX core, which is
responsible for creating and tracking the execution semantics of each job in
the system.
Developer and end user tools are on the periphery of WSMX. Various de-
veloper tools have already been presented that aid the design-time process