"Effective" entities are those that are not splitted into subbentites (leaves). They are "terminal" elements of the project, i.e., elements that designate an "effective" work to perfom.

As an example, if a task A is splitted into two tasks B and C performing B and C will realize A. The real work which has to be done is the work defined by B and C. Here we conclude those tasks are "effective".

This definition can be generalized to the entire entity set managed by the project manager: Final requirements can also be qualified as "effective", thus being those on which the final delivery checkup will concentrate its sight.