This file is actually a python source file that defines the tuples builds, arches and subarches. These variables tell buildrepo which builds, arches and subarches it should manage. A map_build() function is also defined which buildbot uses to determine what kind of build to perform. The arguments passed to the function are based on the last successful build. The function can read these arguments and return a string to define the type of the next build. In the above example, the map_build() function will cause the next build after a freshen build to be a full build, and the next build after a full build to be a freshen build, so that the build will alternate between full and freshen.