Which SOA Approach Do You Favor: Top-Down or Bottom-Up?

I believe a combined approach at the planning level is required to be successful. However, once the business and the IT function have decided what they wish to achieve, it is my view that the technical implementation must start at the bottom up. The key to any business is its raw data; how this is presented at the upper levels either via GUI applications or BPM processes, the data is king. Many organizations try to build a SOA on already complex layers to access their existing data and business logic within their organizations. If the principles of SOA go right to the existing data and business logic in an organization, it will provide a much better foundation upon which the business process may be mapped in a SOA implementation. While it's possible to build this data/business logic access layer in many ways, I would argue that using a standards based approach will ensure that whatever the business requirement, the low level business/data access objects that are built will be reusable again and again.

The answer can be found in addressing a similarly structured question: In an artistic endeavor, which color do you favor: Red, Green, or Blue? If you're not color blind, then most answer with "Well, All. It depends upon what I am creating." Top-down, bottom-up, inside-out, or even outside-in are all architectural characteristics of solution structures, designed to be the means to the end and not the ends in themselves. Just as the artist who starts with all colors on their pallet, so should an architect when addressing most enterprise issues.

SOA is architectural style. Building architecture is Top-Down and not Bottom-Up. Web Service, sometimes wrongly defined as SOA, are technical. Web Services are build Bottom-Up. Building SOA Bottom-UP is a wrong approach some times called ABOS (A Bunch Of Services). If you build SOA Bottom-Up probably you will end with a lot of redundancy and no architecture at all. However, the result of building SOA only Top-Down could be perceptual Architecture building with no run time artifacts, so some SOA efforts should be Bottom-Up efforts. To sum up: Initially SOA is a Top-Down approach but pragmatic approach requires mixing Top-Down approach with Bottom-Up approach.

These days, as demonstrated through the power of social networking, employees and professionals have the impetus for organizational change. They are closest to the customers, they know what's needed to do their jobs better. The creation and proliferation of services via SOA needs to be a bottom-up movement. CEOs, CFOs and CIOs need to set the tone and vision, then get out of the way.

If you start constructing service from what you have - bottom-up - you have a very high risk to end up with what you have, not with what your consumers need.

SOA is the consumer-centric business-oriented architecture. Starting with the consumer needs you do not have a chance to avoide the top-down. This is the start point, always. However, in the next step, you better assess your capabilities, i.e. look at the consumer needs from your bottom laying recources.

WHat would be the lable for described approach?