UML class diagrams (UCDs) are a widely adopted formalism
for modeling the intensional structure of a software system. Although
UCDs are typically guiding the implementation of a system, it is common
in practice that developers need to recover the class diagram from an
implemented system. This process is known as reverse engineering. A
fundamental property of reverse engineered (or simply re-engineered)
UCDs is consistency, showing that the system is realizable in practice.
In this work, we investigate the consistency of re-engineered UCDs, and
we show is pspace-complete. The upper bound is obtained by exploiting
algorithmic techniques developed for conjunctive query answering under
guarded Datalog+/-, that is, a key member of the Datalog+/- family
of KR languages, while the lower bound is obtained by simulating the
behavior of a polynomial space Turing machine.