Wednesday, May 20, 2009

Service Component Architecture

Discussing about agile IT architecture on this blog without going to SCA will be a major error. I'm playing with SCA since last September, and I love it.
Service Component Architecture is defined as the implementation of the SOA architecture. You can read an excellent paper from David Chappell on this subject. SCA separates application business logic and the implementation details. It provides a model that defines interfaces, implementations, and references in a technology neutral way, letting us to bind these elements to any technology specific implementation.

For the business case and business user point of views the value propositions are around:
- Save time and money
- A simpler API, Efficient GUI tools to assemble components to build new application
- Enable and encourage reuse - Developers can create composites that perform useful functions. SCA makes it easy to use and reuse business logic.
- Bring agility to interchange business logic
- Bring visibility on how the application is built. I can imagine easily using the assembly diagrams to explain how 'business' components work together in the context of the current application.

On the architecture level the ability to separate business logic from infrastructure logic reduces the IT resources needed to build an enterprise application, and gives developers more time to work on solving a particular business problem rather than focusing on the details of which implementation technology to use.
Some key concepts:
A component implements some business logic exposed as one or more services that operate on business data. Component includes an implementation, and can have partner references and interfaces.

A component can indicate the services it relies on using references. Explicitly defining references allows dependency injection, the SCA runtime can locate the needed service and injects the reference into the component which needs it.
Components are bring together within an assembly or composite. The composite is persisted as an XML document using the Service Component Description Language (SCDL).

A component can also define one or more properties. Each property contains a value that can be read by that component from the SCDL configuration file when it’s instantiated. Finally a domain can contain one or more composites, each of which has components implemented in one or more processes running on one or more machines.

On the tools and implementation side, IBM for sure has an impressive offering on that space with WebSphere Integration Developer. Apache Tuscany is also an excellent open source to help us jumping into the technology and understand how it works. Eclipse Ganymede is offering an assembly editor, SCA project plugin...

We will build our AML application using SCA

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