SOA is an approach to building complex software systems from reusable services following service-oriented principles. SOA is also a component model, which links different functional units (called services) of applications through well-defined interfaces and contracts between these services. The interface is defined in a neutral way, which should be independent of the hardware platform, operating system and programming language that implements the service. This enables services built in a wide variety of systems to interact in a unified and common way.
SOA can distribute, combine and use loosely coupled coarse-grained application components through the network according to requirements. The service layer is the foundation of SOA, which can be directly invoked by applications, thus effectively controlling the human dependencies caused by the interaction of software agents in the system.