Sunday, February 14, 2010

Limiting Irreversibility

This afternoon I was reading Martin Fowler's commentary on architecture:, and ran across the following:

At a fascinating talk at the XP 2002 conference (, Enrico Zaninotto, an economist, analyzed the underlying thinking behind agile ideas in manufacturing and software development. One aspect I found particularly interesting was his comment that irreversibility was one of the prime drivers of complexity. He saw agile methods, in manufacturing and software development, as a shift that seeks to contain complexity by reducing irreversibility—as opposed to tackling other complexitydrivers. I think that one of an architect’s most important tasks is to remove architecture by finding ways to eliminate irreversibility in software designs.

I think he's absolutely on the mark with this--in fact, I think it illuminates one of the two or three key roles of architecture in system implementation. If the architect focuses on helping to define approaches which are hard to change once the system "complexifies", and in helping developers write solid code that can easily be modified when needs change, (s)he goes a long, long way towards making the system flexible and maintainable.

Note that there's two architectural roles there: (1) helping to make key decisions early, and (2) mentoring developers around those decisions.

On most of the dev teams I've worked with, the first set of decisions is made by proposal and refinement--one of us proposes an overall approach, and the rest of us point out tweaks or whole new approaches until the whole thing gels in everyone's mind. It seems to work, if everyone is engaged. Some architects would prefer to "rule by fiat", but I've found that generally results in systems which can't be maintained or in far more work than is needed. It's very hard to get key decisions right by yourself. To illustrate: I once proposed a relatively modest refactoring in a large thorny user interface, to separate business logic from display logic and generally make it easier to maintain. The reigning architect decided we needed a complete rewrite, in direct opposition to the opinion of everyone else on the team. Nobody objected strongly, though everyone quietly agreed that a rewrite probably wasn't needed--it's lot more fun to write new code than to modify old. Nobody asked what the minimum effort needed to meet the requirements was. About two years and a couple million dollars later, the new system is, indeed, quite a bit better-structured than the old one. It's not clear if the new UI will produce allow faster, cleaner updates than the old one--but it sure cost a lot to build: about twice the initial estimate, and about 6 times the original proposal. (By the way: the rewrite is considered a success by all involved. See "What Could Possibly Be Worse Than Failure?" by Alex Papadimoulis.)

A second role implied in minimizing irreversibility is "mentor". Writing good code is hard; writing well-structured code without someone to bounce your design off of is doubly hard. I spend a lot of time talking with the members of my teams, trying to make sure we have a design that's flexible and understandable. A lot of what we think of as "architecture" starts out as a small feature being implemented by a relatively junior developer. I try to make sure (s)he has someone to work with in the early stages of that work, or at least a trial design to start from.

I love Martin Fowler's writing: he always gives me something good to think about.

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