Top down or Bottom-up SOA
Having seen both the SOA approaches top down and as well as bottom-up, this question still bewilders me if there is any right option out of these two? There is no easy answer. Or I would like to believe it depends...
We all know business will endorse any new investments only if they see a quick and healthy return from it, whereas architects will always be tempted to choose solutions on new technologies requiring budgets. It becomes rather challenging to make both the approaches meet at a common point in case of Service- Oriented Architecture. If SOA is only about building business services and only a paradigm change, then why do these initiatives fail? Is it because organizations start from bottom-up whereas they should be doing it top down or is the case the other way?
Top down approach requires a lot of strategy formulation, a strong commitment from management, CIO, all LOB heads to come together to define candidates for services and requirements for these services. It’s typically a long road map between 2 years to 3 years with significant budgets pre-approved. The pitfall is the speed at which IT can work, otherwise it will never be achieved due to usual operational distractions; frequent changes in the business requirements; disagreement between stakeholders and soon you will hit a roadblock.
Bottom-up on the other hand, starts with building a service layer quickly without having any dependency on business. Business does not drive it, IT drives it. A service layer is built around stable systems like legacy and this approach is further extended gradually to all systems. Each project is independently approved. This can work effectively. However, in a larger setup with multiple LOBs bottom-up method ends up as a fiasco as semantic differences are so huge that the services which were built in incremental projects prove hardly reusable. If each LOB starts working bottom-up, the enterprise will end up as fragmented SOA instead of integrated.
I have seen a lot of blogs recommending a mix of both these approaches, but wouldn’t it be even more difficult to achieve? I believe if the size of your organization is small, the bottom-up approach can work well. But for a medium to large size enterprise, top down will be almost unavoidable. A well defined governance model will be another force to go in for the top down approach.
I would love to hear from you if you have experience in top down or bottom-up SOA.
Top down approach requires a lot of strategy formulation, a strong commitment from management, CIO, all LOB heads to come together to define candidates for services and requirements for these services. It’s typically a long road map between 2 years to 3 years with significant budgets pre-approved. The pitfall is the speed at which IT can work, otherwise it will never be achieved due to usual operational distractions; frequent changes in the business requirements; disagreement between stakeholders and soon you will hit a roadblock.
Bottom-up on the other hand, starts with building a service layer quickly without having any dependency on business. Business does not drive it, IT drives it. A service layer is built around stable systems like legacy and this approach is further extended gradually to all systems. Each project is independently approved. This can work effectively. However, in a larger setup with multiple LOBs bottom-up method ends up as a fiasco as semantic differences are so huge that the services which were built in incremental projects prove hardly reusable. If each LOB starts working bottom-up, the enterprise will end up as fragmented SOA instead of integrated.
I have seen a lot of blogs recommending a mix of both these approaches, but wouldn’t it be even more difficult to achieve? I believe if the size of your organization is small, the bottom-up approach can work well. But for a medium to large size enterprise, top down will be almost unavoidable. A well defined governance model will be another force to go in for the top down approach.
I would love to hear from you if you have experience in top down or bottom-up SOA.
