Friday, September 09, 2011

What does "Top-Down" mean?

#entarch There seem to be several different ways people use the term “top-down”.
  • Management hierarchy. Top-down means traditional command-and-control. See my post on Multiple Styles of EA.
  • Decomposition/Refinement. Top-down means starting from broad vision and principles; bottom-up means starting with concrete detail and evidence.
  • Large versus small. Top-down means starting with the big pieces and assuming that the small pieces can be fitted into the gaps left by the big pieces.  See Nick Malik's piece Should SOA be Top Down or Bottom Up, which I discussed in my post on Service Planning.
  • Planned versus emergent. Top-down means directed and planned, bottom-up means collaborative and emergent. See my post on Emergent Architecture.
  • TO-BE versus AS-IS. Top-down means starting from the future requirements of the business; bottom-up means starting from the available assets.
In very simple cases (such as the examples given in the books and training courses), these overlapping but logically distinct meanings of “top-down” may happen to coincide; but as things get more complex, the tension between competing notions of “top-down” will become more significant.

In a debate on community regeneration, Matthew Mckeague writes "What I don’t think can be forgotten in the ‘bottom up’ ‘top down’ debate is that it shouldn’t be a binary choice. There’s a balance to be struck and professional skills and networks can’t be underestimated. It’s where the balance sits that we need some further debate."

See also The Politics of "Top-Down"

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