What is SOA?

The concept of a service is nothing new, but the notion of an SOA has evolved over the past couple of years. It's an architectural style of building software applications that promotes loose coupling between components so that you can reuse them. Thus, it's a new way of building applications with the following characteristics:

• Services are software components that have published contracts/interfaces; these contracts are platform-, language-, and operating-system-independent. XML and the Simple Object Access Protocol (SOAP) are the enabling technologies for SOA, since they're platform-independent standards.
• Consumers can dynamically discover services.
• Services are interoperable.

Figure 1 gives a overview diagram of service-oriented architecture.

The basic building block of SOA is the service. A service is a self-contained software module that performs a predetermined task: "verify a customer's credit history," for example. Services are software components that don't require developers to use a specific underlying technology. As Java developers, we tend to focus on reusing code; thus, we tend to tightly integrate the logic of objects or components within an application. However, SOA promotes application assembly because services can be reused by numerous consumers. For example, in order to create a service that charges a consumer's credit card, we build and deploy only one instance of such a service; then we can consume this service from any number of applications.

The other key advantage of SOA is that it lets you automate business-process management. Business processes may consume and orchestrate these services to achieve the desired functionality. Thus, new business processes can be constructed by using existing services. For example, a customer order that has been submitted to shipping can be represented by a business process that can asynchronously interact with the requisite services.

Why SOA?

Today's IT organizations invariably employ disparate systems and technologies. Most analysts predict that J2EE and .NET will continue to coexist in most organizations and the trend of having heterogeneous technologies in IT shops will continue. Moreover, creating applications that leverage these different technologies has historically been a daunting task. SOA provides a clear solution to these application integration issues by allowing systems to expose their functionality via standardized, interoperable interfaces.

Using SOA offers several key advantages. You can:

• Adapt applications to changing technologies.
• Easily integrate applications with other systems.
• Leverage existing investments in legacy applications.
• Quickly and easily create a business process from existing services.