A service-oriented architecture (SOA) is a style of software design where services are provided to the other components by application components, through a communication protocol over a network. The basic principles of service-oriented architecture are independent of vendors, products and technologies.[1] A service is a discrete unit of functionality that can be accessed remotely and acted upon and updated independently, such as retrieving a credit card statement online.
A service has four properties according to one of many definitions of SOA:
It logically represents a business activity with a specified outcome.
It is self-contained.
It is a black box for its consumers.
It may consist of other underlying services.
Different services can be used in conjunction to provide the functionality of a large software application.
So far, the definition could be a definition of modular programming in the 1970s. Service-oriented architecture is less about how to modularize an application, and more about how to compose an application by integration of distributed, separately-maintained and deployed software components. It is enabled by technologies and standards that make it easier for components to communicate and cooperate over a network, especially an IP network.