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Thursday, April 08, 2004

Robert O'Brien; an economic metaphor for constrained interfaces 

Via Mark Baker
The expressive power of an information system is proportional not to the number of objects that get implemented for it, but instead is proportional to the number of possible effective interactions between objects in it. (Reiser's Law Of Information Economics)

This is similar to Adam Smith's observation that the wealth of nations is determined not by the number of their inhabitants, but by how well connected they are to each other. He traced the development of civilization throughout history, and found a consistent correlation between connectivity via roads and waterways, and wealth. He also found a correlation between specialization and wealth, and suggested that greater trade connectivity makes greater specialization economically viable.

You can think of namespaces as forming the roads and waterways that connect the components of an operating system. The cost of these connecting namespaces is influenced by the number of interfaces that they must know how to connect to. That cost is, if they are not clever to avoid it, N times N, where N is the number of interfaces, since they must write code that knows how to connect every kind to every kind.

One very important way to reduce the cost of fully connective namespaces is to teach all the objects how to use the same interface, so that the namespace can connect them without adding any code to the namespace. Very commonly, objects with different interfaces are segregated into different namespaces.

If you have two namespaces, one with N objects, and another with M objects, the expressive power of the objects they connect is proportional to (N times N) plus (M times M), which is less than (N plus M) times (N plus M). Try it on a calculator for some arbitrary N and M. Usually the cost of inventing the namespaces is much less than the cost of the users creating all the objects. This is what makes namespaces so exciting to work with: you can have an enormous impact on the productivity of the whole system just by being a bit fanatical in insisting on simplicity and consistency in a few areas.


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