An service oriented architecture (SOA) is an architectural pattern – or a principle – where sub-systems can be perceived as services, which can be used in different contexts and independent of technological platforms. It is important to remember that SOA isn’t a product or a concrete implementation.
SOA is characterized by the following:
Loose coupling is probably the main principle behind SOA and is the primary precondition for a flexible IT platform where the services can be reused or linked across systems. When an application has to use a service from a service provider, the service is identified from a description that among others includes input and output data and location. That way there are no direct linkage between service provider and service consumer.
A basic belief in the service-oriented way of thinking is the notion that services can be provided and used without consideration of the underlying technology. This makes demand on open technological standards. International standardization agencies are involved in comprehensive standardization work which has created and will create the foundation for a realisation of SOA without tying it to a specific provider or technology. Open standards are thereby a precondition for realizing an actual loose coupling between the systems.
The user of a certain service does not need to know its physical location. The description of the service contains a reference to the actual location and can be changed without affecting the application which uses the service. That means that the interaction between applications is no longer dependent of physical system architecture.
Services are the abstraction between business processes and technology in SOA. To get the full value out of the principals behind SOA it is necessary to adapt a process orientated approach to the architecture. The business processes have to be related to high level coarse grained services which on the other hand has to be related to more fine-grained services that often consist of exposing components in current solutions.
The implementation of SOA gives the organisation a high degree of flexibility which makes it possible to react quickly to changes. One area can for example be moved to another organization or be outsourced to an external provider. The company thereby gets the possibility to place tasks where they are solved most easily and tactical decisions can be assessed in a strategic perspective.