Information Technology Reference
In-Depth Information
Subsystem
X
Subsystem
Y
System A
Wire
Subsystem
B
Subsystem
D
Wire
Subsystem C
Wire
Module
component E
Module
component F
Wire
Implementation
Module G
Module H
Figure 5.1
An example of system assembly and disassembly.
The main difficulty of deploying services under SCA is that there
are multiple service assembly methods and many configuration choices
interweaved to satisfy both functional and nonfunctional requirements.
We model the configuration problem as service functional configuration
(SFC). A Web service may have multiple SFCs, for example, in Fig-
ure 5.1, system A can be configured by wiring subsystems B, C, and D,
or subsystems X and Y. However, only one configuration can be
selected at one time. The optimal choice should meet both a user's
functional and QoS requirements.
As a dynamically formed digraph to present all of the references,
service dependency graph (SDG) is popularly used to depict the
functional dependency relationship among Web services [125]. How-
ever, although SDG provides a means for Web service configuration
descriptions in order to ensure functional interoperability among
collaborating Web services, it deals with only the functional aspect.
It can hardly support the dynamic configuration of Web services to
deal with nonfunctional requirements. Moreover, the SCA specifica-
tion set being developed under the open SOA collaboration [32] and
most of the current research on SCA does not incorporate QoS [126].
