SOA separates business functions into distinct units, or services. A SOA application reuses services to automate a business process.

A standard interface and message structure define services. The most widely used mechanism are web services standards. These standards include the Web Service Description Language (WSDL) file for service interface definition and XML Schema Documents (XSD) for message structure definition. These XML standards are easily exchanged using standard protocols. Because standards for web services use a standard document structure, they enable existing systems to interoperate regardless of the choice of operating system and computer language used for service implementation.

When designing a SOA approach, you create a service portfolio plan to identify common functionality to use as a service within the business process. By creating and maintaining a plan, you ensure that existing services and applications are reused or repurposed whenever possible. This plan also reduces the time spent in creating needed functionality for the application.