Concurrent Versions System, A Method for Independent Cooperation

People working together on a set of files in real-world circumstances may often interfere with each other. To avoid such interference, the idea of an abstract data type can be used. The abstract data type introduced here consists of a single repository, containing versions of the files, together with a (small) number of access routines. Each participant has his own copy of a set of files as represented by the repository, and uses essentially two access routines, one to merge into his copy changes made to the repository by others, and one to merge changes in his copy into the repository. (There are several other access routines, for listing contents, examining differences, etc.) The abstraction is not perfect, but violations (conflicts) are gen- erally detected and reported. The implementation of the abstract data type "repository" starts from version control primitives that can handle a single file and then coordinates their actions. All access routines are programmed as UNIX† shell scripts and use the RCS programs as version control primi- tives. In programming the access routines, many more possibilities had to be taken into account than was intuitively reasonable. Examples are given.