The upper process flow digram presents the main principle of merge tools in software configuration management. When a source file is required by a second workespace, the center DB will deliver a copy of that file to it. And after submitting the 2 versions of the same file, merger tools will start to combine these two version into a new one. It is based on a line by line process, which is: if There are new lines in the submitted version, add them to the source file, and if there are lines which do not exist in the new version, delete these lines in the source file. After several times of iteration, a new version of the sources file, which contains all the changes created by the two (or more) authors, will be upload again to the central DB and acts as a new version of the source file.