SOA PRINICIPLES

Service-Oriented Architecture Principles
1)Explicit boundaries
    SOA is all about messaging—sending messages from point A to point B. These messages must be able to cross explicit and formal boundaries regardless of  what is behind those boundaries. This allows developers to keep the flexibility of how services are implemented and deployed. Explicit boundaries mean that a service can be deployed anywhere and be easily and freely accessed by other services, regardless of the     environment or development language of the other service.there is a cost associated with  crossing boundaries. These costs come in a number of forms, such as communication, performance, and processing overhead costs. Services should be called quickly and efficiently.
2)Autonomous services
    Services are built and deployed independently of other services. Systems, especially distributed systems,must evolve over time and should be built to handle change easily. This SOA principle states that each service must be managed and versioned differently so as to not affect other services in the process.
3)Policy-based compatibility
    Each service may or may not have certain requirements before it will start communicating and handing out information. Each service has its own compatibility level and knows how it will interact with other services.Services look at each others’ policy, looking for similarities so that they can start communicating. If two services can’t satisfy each others policy requirements, all bets are off. These policies exist in the form of machine-readable expressions.Policies also allow you to move a service from one environment to another without changing the behavior of the service.
4)Shared schemas(data) and contracts (behavior).
    The contract contains information regarding the structure of the message. Services do not pass classes and types;they pass schemas     and contracts. This allows for a loosely coupled system where the service does not care what type of environment the other service is executing on. The information being passed is 100 percent platform independent.