Service-oriented architecture (SOA) is one of those phrases that gets thrown around in everything from technical standards to business books. Thomas Erl makes four key points in his books: 
- SOA can establish an abstraction of business logic and technology that allows a looser coupling between an organization's processes and its technology.
- SOA is an evolution of past approaches, preserving successful characteristics of traditional architectures and adding distinct new principles that foster service orientation.
- SOA is ideally standardized throughout an enterprise, but achieving this requires a planned transition and still-evolving technology.
- SOA is a technology architecture that supports and promotes service-oriented principles throughout an enterprise.
What SOA does, at a fundamental level, is allow the development of individual pieces of business functionality in a way that lets them be combined and modified effectively and without tightly coupling them to each other.
 Thomas Erl. Service-Oriented Architecture (SOA): Concepts, Technology, and Design. Prentice-Hall (2005).