David Parnas

David L. Parnas is one of the great software philosophers.

Author of the seminal paper "On the Criteria To Be Used in Decomposing Systems into Modules" (see OnDecomposingSystems), http://www.acm.org/classics/may96/, which ends as shown below.

"We have tried to demonstrate by these examples that it is almost always incorrect to begin the decomposition of a system into modules on the basis of a flowchart. We propose instead that one begins with a list of difficult design decisions or design decisions which are likely to change. Each module is then designed to hide such a decision from the others. Since, in most cases, design decisions transcend time of execution, modules will not correspond to steps in the processing. To achieve an efficient implementation we must abandon the assumption that a module is one or more subroutines, and instead allow subroutines and programs to be assembled collections of code from various modules."

I only recently noted the attention to the loss of performance given by his modularization.

He also wrote the classic "A rational design process: how and why to fake it".

Some of his papers are collected into the book SoftwareFundamentals.


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