Portal and Workflow in Grid Computing: From Application Integration to Service Integration - Grid Computing: Infrastructure, Service, and Applications - page 290

development and maintenance of a workl ow can be simplii ed. However,
the understanding of SOA still remains at a conceptual level to many users.
In order to help realize the SOA, IBM has proposed a new programming
model, namely, service component architecture (SCA). SCA is a set of speci-
i cations that describe a model for building workl ows, applications, and
systems using SOA [1]. It now gets supported by many companies such as
Oracle, Sun Microsystems, and BEA. SCA is based on the standard Web
services and provides a model for service integration and creation of ser-
vice components, including the reuse of existing application functions
within SCA compositions. The IBM workl ow engine WebSphere Process
Server, and the associated workl ow development toolkit WebSphere
Integration Developer use the SCA programming model.
The SCA programming model is briel y described as follows [63]:

• Module —the module is a container for service components. It is a

deployment unit and packaged as an EAR (Enterprise ARchive).
Component • —the service component is a basic building block in

SCA, as shown in Figure 11.2. Each component has got interface,
reference, and implementation.
Interface

• —the interface is a specii cation of component's opera-

tions, which contains input, output, and faults. It can be dei ned
using Java or WSDL.
Reference • —when implementing a service component, another

service component may need to be invoked. This is realized
through reference. A reference indicates what interface the called
component should ultimately have. The calling component can
have one or more reference. The reference can be expressed using
Java or WSDL.
Wire • —a wire is simply a connection that indicates which refer-

ence is connected to which component.

Java Java

SCA Service
Component

I R

Reference

WSDL Interface WSDL

Implementation

FIGURE 11.2 SCA service component model. (Adapted from S. Penugonda and P.K.
Dash, “SCA application development, Part 1: An overview of service component
architecture,” IBM developerWorks , August, 2006.)