The purpose of a build, constructed from other elements in the implementation, is to deliver a testable subset of the run-time functions and capabilities of the system. The Rational Unified Process (RUP) suggests that a sequence of builds be constructed during an iteration, adding capability with each, as elements from implementation subsystems are added or improved.  Builds can be constructed at all levels of a system, encompassing single or multiple subsystems, but in the RUP, we are concerned in particular with the builds that are defined in the Artifact: Integration Build Plan, because these are the stepping stones to the completion of the iteration.  If the system size or complexity warrants it, the Integration Build Plan can be refined into multiple plans, covering individual subsystems.

Note that informal builds can be constructed by an implementer for several reasons - unit testing, for example - using elements from the implementer's private development workspace and the subsystem and system integration workspaces, as appropriate. However, as the term is used here, builds are constructed by an integrator, from identified versions of elements delivered by the implementers into the subsystem or system integration workspaces, as defined in the Artifact: Integration Build Plan.