It's an interesting book with a lucid language and simple to understand examples.
Jotting down some of the design principles for SOA:
- Services should be platform neutral and programming language neutral
- Services should have a standard interface contract
- Services should be loosely coupled
- Design for coarse grained services
- Service Abstraction - Hide information that is not required by clients. Hide underlying technology details. Promotes loose coupling.
- Service Reusability - Position services as enterprise resources with agnostic functional context; i.e. the service can be used in other functional scenarios too. Always design the service in such a way, that it can be used beyond its original context.
- Service Autonomy - Services need to have a high degree of control over their underlying runtime execution environment. The higher up a service is in a typical composition hierarchy, the less autonomy it tends to have due to dependencies on other composed services.
- Service Statelesness - defer or delegate state to databases, rather than in memory.
- Service Discovery - services can be discoved using standards such as UDDI.