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Top-Down vs Bottom-Up SOA

InfoQ fired the debate again. When I looked at my past, I see myself sometimes on side, sometime on the other side. Almost exact debate exist between centralized vs decentralized.  Same story. Now that I have more structured thoughts, I can share them.

So, the problem here is not SOA should be top-down or bottom-up.  We need to focus on what needs to be bottom-up and what needs to be top-down. My approach is to go with the layers. Take Zachman, when you look at the upper layers (Scope, Business, System) are more top-down, and the lower layers (Operations, Implement, Develop) are more bottom-up. Of course the line is not very clear, in the middle (System, Develop) bot approaches meet each other.

Depending on the area of interest, people choose different side on the discussion. Bill de hÓra argues SOA cannot be top-down because there’s no top, SOA systems are in reality decentralized. Of course, when he’s talking, he’s thinking about web services, applications, RPC protocols, REST etc. All about implementation of services. He’s 100% right. On this level, decentralization is the key. On the other side he’s failing to understand when John Crupi is telling SOA must be business driven, must be top-down, he means we start with vision/mission, strategy/tactics, not by technology. He’s not talking about implementation, but scope, business and system in Zachman. There, to have top-down approach is the key.

So my conclusion is people either cannot express what they’re talking about and assume everyone else is in the same layer or fail to understand there are different layers and there’s no one approach to use in all of them. As I experience everyday, latter is more common.

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