SOA : Design Principles

The following service oriented principles should be applied to the extent possible so that the benefits of SOA can be realized.

1. Standardized Service Contracts

• A SOAP Web Service has the following as part of the contract
• WSDL
• XSD
• WS Policy
• SLA (Service Level Agreement)
• Service Contract is standardized through the application of design standards(contract first approach)
• Standardized naming conventions(expressive)
• Standardized data types(reduces the transformations between data types)

2. Loose Coupling

The different types of coupling are

• Logic-to-Contract Coupling
• Created when the "contract first" approach is followed
• Tight coupling of Service Logic on the Service Contract
• Positive
• Contract-to-Logic Coupling
• Created when the Service Contract is auto generated from the Service Logic
• The Service Contract is dependent on the underlying Service Logic
• Also, auto generation of schemas from the database tables
• Negative

3. Service Abstraction

• Hides the implementation details from the Service Consumers(to be hidden - includes technology, functional, programmatic logic and quality of service information)
• This provides the freedom to evolve the service implementation as required.

4. Service Reusability

• Services should contain and express agnostic logic so that they can be reused across the enterprise.
• Achieving this is very important as the ROI is highly dependent on the degree of reuse achieved
• Some of the design characteristics are
• The Service is defined by an agnostic functional context
• The Service Logic is highly generic
• The Service Contract is generic and extensible
• The Service Logic can be accessed concurrently

5. Service Autonomy

• The level of control over the underlying runtime execution environment.
• Task Services have less autonomy as they compose other services over which they have less control.

6. Service Statelessness

• Stateless Services
• Increase Service Scalability
• Increase Service Reusability
• Consume less computing resources
• Orchestrated Task Services are expected to be stateful
• Entity and Utility Services are generally stateless

7. Service Discoverability

• Services are supplemented with meta data by which they can be effectively discovered

8. Service Composability

• Services should be composable