Improving computer program readability to aid modification
James L. Elshoff, Michael Marcotty · Communications of the ACM · 1982
The Modification CycleThe modification of computer programs is a costly and constant job.An informal survey conducted at General Motors and reported on by Elshoff [6] concluded that about 75 percent of all programmer/analysts' time in a commercial data processing installation is spent on program modification.This conclusion agrees with independent assessments made by Liu [16], Boehm [2], and Lientz and Swanson [15].Moreover, the reasons for modifying programs will not disappear.As pointed out by Lehman [14], all programs are models of some part of the real world and, as the world changes, programs must be modified to keep pace with these changes or they become progressively less relevant, less useful, and less cost-effective.As new software is developed, the inventory of programs to be maintained grows, and thus this high level of modification work is not expected to decrease.The modification cycle is composed of a sequence of steps such as:(l) The user requests that a program be changed.(2) The specifications for the change are written and the cost of the change estimated.(3) It is decided that the changes are worth being made.(4) The program is changed to meet the new specifications.Unfortunately, the modification environment is not as simple as this list.The frequency of change, the extent CR Categories and Subject Descriptors: D.