Sunday, December 10, 2006

Service Planning 2

Nick Malik asks Should SOA be Top Down or Bottom Up. He suggests that architects need to pay attention to the big pieces and can ignore the small pieces.
"While the architects do not need to know about every moving part, they DO need to be aware of the largest of those parts, and make sure that they are managed well. This is similar to city planning, where the city needs to work with a large employer or a large retailer (like Walmart) to make sure that roads and parking and congestion issues are managed, without having to worry about cafe and card shop that are also employers, but have a minimal impact on the infrastructure."

Some people argue for a "fractal" notion of the service economy. While the word "fractal" isn't always used in its precise mathematical sense, its use seems to imply that the service portfolio should have a good mixture of different sizes / granularities (although not necessarily in the same architectural layer). Such a mix of different sizes is also advocated by Christopher Alexander.

In city planning, small retail outlets such as cafes and card shops may individually have less economic or environmental impact than a major retailer such as Wal-Mart. But collectively, they may have at least as much impact. (This is a "long tail" argument.) One of the challenges for city planning is to achieve a good balance between the large few and the many small. (Of course this raises questions of governance as well as architecture, politics as well as economics.)

If the total weight of the large pieces is greater than the total weight of the small pieces (whatever measure we choose for "weight"), then this is itself an architectural choice, with important implications for project agility and enterprise agility.

Most people in this game think they know what the terms "top-down" and "bottom-up" mean, but these terms are commonly used in different (contrary, confusing) ways. If an architect only worries about fitting the big pieces together, and assumes that the small pieces will somehow look after themselves in the remaining ("negative") space, this sounds like one version of what some people would call "top-down".

What if the architect concentrates on providing "positive space" in which the small pieces can thrive, and prevents the big pieces from encroaching on this space. What if the architect concentrates on the interfaces between the pieces, rather than the pieces themselves. Is this "top-down" or "bottom-up"?

I don't really care what we call this - although it would be good to have a more precise way of talking about it - but I think this is an equally valid strategy.

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