Information Technology Reference
In-Depth Information
functions required by the orchestration. It is often done under
Service Component Architecture (SCA). On the other hand,
service composition is mainly process-oriented and provides
the higher-level orchestration. Compared with process-ori-
ented service composition, function-oriented service configu-
ration enjoys more agility and flexibility. For example, if a
Web service is configured by two services, these two services
may be executed in sequence or parallel depending on their
implementation. Moreover, service configuration under SCA
can protect business logic and improve testability, for exam-
ple, configuration information can be used by service fault
management to track defects. SCA builds on service encap-
sulation through the assembly of heterogeneous services.
After the components that provide services and consume
other services are implemented, they are assembled to build
the business application through the wiring of service refer-
ences to services [124]. An SCA module is assembled by
configuring and wiring together components, entry points, and
external services. Entry points are the representation of inter-
faces that are offered for use by components outside a module.
If a component in a module references the services provided
outside of it, they are represented as external services. SCA
assembly operates at two levels, that is, the assembly of
loosely connected components within a system and within
a module. A dynamic configuration can be modeled as a
functional assembly of the overall requested function. For
example, in Figure 5.1, system A can be wired by subsystems
B, C, and D, or wired by X and Y. Subsystem C can be wired
by module components E and F, whereas E has two candidate
modules G and H for its implementation. The SCA configu-
ration also becomes a service, which can be accessed and
reused in a uniform manner. Multiple service components can
be configured and assembled into groups called composites, to
provide specific business capabilities that can be a part of
other services. For example, C in Figure 5.1 can be a com-
posite and can be referenced by other services. Since the
assembly of an SCA system mirrors the assembly of a module,
we
do
not
distinguish
among
subsystems,
modules,
and
services in the topic.
