Information Technology Reference
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Figure 7.5 Four plug-ins in Taverna service panel. The four plug-ins in caGrid workflow
toolkit are as follows: caGrid-activity ( caGrid service . . . and caGrid service from
WSDL . . . ) for service discovery, invocation, and security enforcement; cql-builder
( CQL Builder ) for the visualized construction of CQL clause to query data services;
caGrid-transfer-activity ( caGrid Transfer Activity ) for file transfers between clients and
services; and cds-activity ( CDS Activity ) for credential delegation.
Service Discovery. In a typical service-oriented infrastructure
such as caGrid, the address of a service of interest is not usually known
to the end users. This makes the task of locating appropriate services a
challenge for users, given the fact that caGrid now comprises more than
100 services storing different data or providing varied analysis capabili-
ties, which are deployed at geographically distributed institutions.
On top of the Globus Index Service [188], caGrid provides the
mechanism to discover services of interest by querying a live service
registry. All the caGrid services are required to publish the metadata that
describe their functionality using WSRF. This information is aggregated
in the registry Index Service and used to find out information about the
currently running services and their currentWSDL addresses. Clients can
then query this aggregated information using standardWSRF operations.
The services' descriptive metadata include service name, WSDL,
hosting research center, operations with associated data types, and
the semantic annotation on the aforementioned metadata, as shown
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