On the Criteria to Be Used in Decomposing Systems into Modules

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David Lorge Parnas
Communications of the ACM 15(12), pages 1053–1058
December 1972

This paper discusses modularization as a mechanism for improving the flexibility and comprehensibility of a system while allowing the shortening of its development time. The effectiveness of a “modularization” is dependent upon the criteria used in dividing the system into modules. A system design problem is presented and both a conventional and unconventional decomposition are described. It is shown that the unconventional decompositions have distinct advantages for the goals outlined. The criteria used in arriving at the decompositions are discussed. The unconventional decomposition, if implemented with the conventional assumption that a module consists of one or more subroutines, will be less efficient in most cases. An alternative approach to implementation which does not have this effect is sketched.

keywordssoftware design, modularity, software engineering, KWIC index, software, modules
journal or series
book Communications of the ACM (CACM)