Information Technology Reference
In-Depth Information
or from a third party, for example, service reputation. Such
information should be collected in a fair manner.
2.
Composition of Web services according to QoS requirements.
Web service composition has to deal with behavioral interface,
choreography, and orchestration. Behavioral interface denotes
the behavioral aspects of the interactions for a given individual
service during the composition. Orchestration considers one
particular service that directs the logical order of all other
services, whereas choreography considers the case where indi-
vidual services work together in a loosely coupled network.
They are often accomplished via Business Process Execution
Language (BPEL). The QoS of the composed service is
determined by the QoS of its underlying component services.
The aggregation functions for the computation of the QoS
through component services need to be identified. It is not
hard to imagine that there may be many feasible Web service
compositions that can meet the functional requirement but
carry different QoS values. Therefore, the QoS of the resulting
composite service is a determinant factor in satisfying the differ-
ent requirements and preferences of different users. For example,
a user may demand for reliability to be maximized while another
user may demand for total cost to be minimized. Different users
may weigh QoS attributes differently. Thus, it is necessary to
consider the preferences of users and optimize the Web service
composition in terms of the QoS requirements. Various methods
can be utilized.
3.
Dynamic environment where composite services are invoked. It
can be explained from two aspects. First, a service composition
operates under a dynamic and heterogeneous environment, and
its run-time performance fluctuates with the varying quality of
the services. Second, when a Web service becomes unusable or
unreliable, the other Web services in the composition that
interact with it may need to be altered in order to adapt to
the new environment. Various QoS-aware Web service selec-
tion strategies are required.
4.
Web service configuration. Service configuration and service
composition complement each other in nature. The former
is
function-oriented
and
offers
the
lower-level
business
