Thursday, 29 October 2009

Service Classification

Zapthink recently asked the question "Are Services nouns or verbs", and if they can be designed as either, then which is better?

I don't think it is a case of "which is better". Services that expose a process (verb) address different requirements to those that expose an 'entity' (noun) . One is not better than the other. Instead they complement each other.

In CBDI-SAE we classify services according to the type of capability they provide. By focusing each service on a particular type of capability it enables greater modularity, separation of concerns and so on, enabling them to be more easily shared or composed into new services.

For example core business services (entity) provide operations focused on managing the information about a key business resource - like customers, orders, or products. These are independent of the processes that use that information.

Whereas process services provide operations that enable solution assemblers for example to interact with the different steps in the process. In turn the process services then consume the appropriate core business services.

In this way they can change the process service, add new operations and such, or add new processes, but without impacting the core business services.

If you mix these capabilities together you run the risk for example that the entity information is only provided via a specific process. We see this often and it's just too coarse grained and not a very agile approach. Processes have a different change cycle to entities. Many different processes use the same entities. So keep them apart.

Suggesting, as some are, that there is only one type of service and each provides multiple types of capabilities overloads the service and makes it difficult to use or share in different contexts or solutions..

We go further than just verbs and nouns however, and CBDI-SAE classifies service types into Process, Capabilities, Core Business Services, Utilities, Underlying, and Infrastructure .

Appendix A1 of our CBDI-SAE Meta Model for SOA also provides definitions for each type, and also gives an example policy for dependency rules between service types.

In CBDI-SAE we then detail different techniques that are applicable to identifying and specifying each type of service.

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