Well, here they go.
- Many people talk about SOA and Services, but I’ve found in presentations, articles, case studies, working with tools vendors and looking at real implementations, that not everyone understands the concepts quite right. So, I have a couple of posts (here, and here) and a short video in the Architecture Journal (SOA Myths), explaining the types of perceptions people have about the concepts, and why I think they are wrong. I assure you it is a good list, interesting to read. So, that would be my first contribution.
- Now, let’s check on the Service concept. As I mention in the posts, to me a service is a cohesive (and coherent) business functionality offered through a uniform interface. And it is technologically neutral. What does that mean? Well, a service is a plain, homonymous metaphor of a business service, just like the loan service in a bank, or a delivery service of you mail office. As a metaphor, it is driven by the rules of common services, with contracts, processes, protocols, controls and evolutions. Its actual implementation may be whatever, but it should not surface the definition, meaning users of a service do not have to know how the service was implemented to use it, and should not have to learn anything else apart from the rules and protocols of regular business services interactions.
- Now, Orientation. For an architecture, orientation describes the guidelines, principles and decisions that are based on the rules that govern the metaphor behavior. That is, the service one.
- Architecture refers to an actual style that defines the architectural constrains, suitability and consequences of using it.
- So, SOA is an architectural styles whose components, constrains and principles are driven by the service metaphor.
- Service implementation is out of scope. Service metaphor implies business domain. The implementation domain should not surface into the business view, not affect the rules of the metaphor. This is something almost all of implementation fails to accomplish: to use a service you usually must know implementation details, and those are the ones that actually avoid flexibility and change.
- The service contract requires a semantic agreement (standard shared business semantics are a must), functional specification, pre and post conditions and the description of side effects. All that is technologically neutral.
- Lastly, and just for the records: to me, reuse is not a business concept, but an IT one. So, Services should not have as a goal the reusable property. In business, the property is composability. The key is to be able to create higher-level services from composing lower level ones. Reuse is a side effect, and should not be the base for ROI, because it will never make it!
William Martinez Pomares