SOA stands for Service-Oriented Architecture, a flexible set of design principles that allow multiple separate systems from several business domains to inter-operate. Service orientation is a paradigm that frames what you do. Service-oriented architecture (SOA) is a type of architecture that results from applying service orientation. ([From soa-manifesto.org][1] )
Service-oriented architecture (SOA) is a flexible set of design principles used during the phases of systems development and integration in computing. A system based on a SOA will package functionality as a suite of interoperable services that can be used within multiple separate systems from several business domains.
SOA make changes easier i.e. flexibility. Legacy architecture makes Rigid integration. SOA is easy to assemble and easily reconfigurable like building blocks.
SOA works modularly. Assemble any way we want. If any changes require, instead of starting from scratch we can re-use and add new block so, SOA is saving time and money.
The analogy
Imagine a house on the country side, that in many ways is part of a larger community, like a city or town. The city has it's own complex systems for providing water and electricity, handling sanitation, providing transportation and other utilities. The House is the consumer in this model, the City (or community) is the provider and the pipes, sewers, powerlines, optical fibers etc. is the Infrastructure in which they communicate.
This model could loosely be compared to a SOA. The people in the house uses a number of different "applications" like radiators, computers, toilets, lamps, underfloor heating, bathtubs etc. These applications don't care how the city generates the water, creates the electricity or handles the waste as long as it works. The components of the city are generators, water pumps and sanitation areas. It provides the house with all these needs but it's up to the house to use it in what ever way it sees fit.
