The core concept behind Service oriented Architecture (SOA) is that it is focused on enabling design and implementation of business process as individual service components (in the form of software) which is loosely coupled and easily discoverable so that inter and intra business processes can interoperate easily and businesses can adapt to changes very quickly. SOA by itself is not a software technology, but an architectural means to componentize service components (business processes) in a loosely coupled manner.
Implementing Service Oriented Architecture (SOA) – Webservices
SOA is mainly implemented as web services. The basic model for web services contains the service provider, service publisher and service consumer. These are individual entities that hosts specific software based components that acts as a provider service, publishing mechanism or a consumer service. For eg: a Quoting application may consume (consumer) a third party quoting service (provider) and may look up a UDDI (Universal Description Discovery and Integration) or a service broker that publishes the services. The provider publishes it services on the registry (UDDI), consumer polls the directory to consume a specific service and the publisher provides the description on what services are available and how to use it. Once the consumer knows where and how to use a service, it no longer needs the publisher.