Jack Van Hoof has a different view than I regarding the difference between Tiers and Layers.

I am not sure I agree with his view, but it still provides an interesting read. I think the main difference between our respective views is that Jack takes a look from the enterprise-architecture angle which gives him layers like:

  • Technical infrastructure; OS, directory Services etc.
  • Application infrastructure; Apps, Portals, DBMSs
  • Application Landscape; SOA, EDA
  • Bushiness Processes; BPM

Jack uses the term "tier" for layers within the same level of abstraction. For instance, he gives the following examples:

E.g. the layer of business services may be arranged in the tiers: front-office, mid-office and back-office. At the next lower layer, the application layer, services may be arranged in the tiers: UI, business logic and data persistency. The interaction of services between two tiers may be bidirectional (but may also be constrained to unidirectional).
The perspective I have (or at least try to maintain in this blog) is the solution/product line architecture -- basically living within Jack's application layers. So in my view I want to know and differentiate between the difference of having a UI and business logic live on the same machine vs. having them distributed in the world. So I guess in the end both perspectives need to have their place and the problem is (like often is the case) overloaded terms.

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