In large systems where you may have up to a hundred implementation subsystems, it becomes a complex task to plan the
To facilitate integration planning, and manage complexity you need to reduce the number of things you need to think
about. It is recommended that you define meaningful sets of subsystems (build sets or towers), that
belong together from an integration point of view. 'Belong together' in the sense that these subsystems are sometimes
integrated as a group; it does not make sense to integrate just one of the subsystems. For example, all the subsystems
in lower layers that a subsystem needs (imports directly, or indirectly) to execute, could be a meaningful build set.
A build set is defined for the lowest layer if these two subsystem often are integrated as a group. A build set is
defined with all subsystems that are needed to compile and execute subsystem A.
Notice that the build sets can, and will, overlap. Which build sets and their contents you have may vary during the
life of a project.
The purpose of defining these build sets is to make it easier to do the integration planning. Instead of thinking about
individual subsystems you can think about sets of subsystems.