As the name suggests, a Service Oriented Architecture is one where application functionality is packaged as autonomous services that adhere to industry standard interfaces (WSDL, SOAP), and the services are then deployed in an IT architecture that makes for their most effective use.
The component services can be rapidly reused and composited, plugged and played as it were, to create new business offerings and they can be individually upgraded for increased business agility. However, to achieve the promise of a SOA it's imperative that critical non-business logic-related functionality, the foremost of which is security, should also be provided and used as a service. And for this to occur it has to be externalized, accessed, and managed independently from the business logic-related services.
