SOA

you have probably heard the phrase service-oriented architecture (SOA). But what is SOA, and more importantly, why is it of interest to the business integration space? WebSphere Integration Developer applications are implemented using a service-oriented architecture, so let's start by looking at what SOA is and what it means for your application to follow this architectural pattern.

Ideally, you want to be able to reuse your existing IT assets as building blocks or components for new applications. Each building block is a service, which means you can access each one in a standard way without regard to its implementation or location. In an SOA, the business logic is separated from the infrastructure, or "plumbing," so that developers can focus on the implementation and not worry about how the service will be accessed.

Put in simplest terms, services are black boxes; you don't care what goes on inside as long as they perform as advertised. Once you have the black boxes, the next key step is to connect them together into an overall integrated application. The boxes can be Java™ technology, Business Process Execution Language (BPEL), connections or adapters to your legacy systems, or connections to Web services provided by partners. These black boxes are your service building blocks.

Services generally are stateless, which means you do not have to worry about calling them in a certain order or in a specific context. Furthermore, you might want to incorporate the services of your business partners and access those in the same way that you access your own services. You might also want your partners to be able to access your services. With SOA, you can adapt or respond easily to a changing business environment by swapping one service for another, or by calling new services as needed. This makes it easy for transactions to occur between businesses.

What is a standard way to access services? Services have published interfaces, which serve as a contract between the service and the caller. An interface can be described with Web Services Definition Language (WSDL), for example, as in the case of Web services. The interface includes the specification of the data that is to be passed to and from the service. The interface doesn't specify how or with what language the service is implemented. So, you could have a service implemented with Java that makes calls to another service that is implemented with BPEL.

All that is a high level, generic view that sounds nice, but we should get down to how you can realize a service-oriented architecture with WebSphere Integration Developer. In the last article, we described all of the different ways to implement services, but we didn't say much about how the services work together.