Service Analysis: Defining effective Service Oriented Architecture
The 3 prominent methods recommended for Service identification during the service analysis phase are -
1. Top down - Functional decomposition driven approach
2. Bottom up - Business process driven approach
3. Hybrid - Meet in the middle.
Unless it’s a brand new initiative, where there is no dependency on any of the existing IT assets, its very rare to see the Top down approach. The services end up being on the coarser side of granularity while adapting Top down approach and on the finer side of granularity while adapting the bottom up approach. If there is a common representation of the end state in Service analysis then the hybrid approach can be used effectively. However due to the lack of standards in representing services or service interaction diagrams, the end state does not conform to a common representation.
Grouping similar services into logical units of components in a bottom up approach or identifying components and then services in a top down approach is a very effective way and works very well in defining SOA based projects. Modeling all 4 architecture models business, application, technology and data coupled with Model Driven Architecture (MDA) helps in identifying the right business and technology components. In a bottom up approach grouping services in components after rationalization helps align with the business architecture. If you think through this thought you will realize that this is an effective combination of Enterprise Architecture framework with a Solution Architecture framework, resulting in a Service Oriented Architecture!
