Unavoidable Boundary Conditions: a Control Perspective on Goal Conflicts

Boundary conditions express situations under which requirements specifications conflict. They are used within a broader conflict management process to produce less idealized specifications. Several approaches have been proposed to identify boundary conditions automatically. Some introduce a prioritization criteria to reduce the number of boundary conditions presented to an engineer. However, identifying the few, relevant boundary conditions remains an open challenge. In this paper, we argue that one of the problems of the state of the art is with the definition of boundary condition itselfit is too weak. We propose a stronger definition which we refer to as Unavoidable Boundary Conditions (UBCs), which utilizes the notion of realizability in reactive synthesis. We show experimentally that UBCs non-trivially reduce the number of conditions produced by existing boundary condition identification techniques. We also relate UBCs to existing concepts in reactive synthesis used to provide feedback for unrealizable specifications (including counter-strategies and unrealizable cores). We then show that UBCs provide a targeted form of feedback for repairing unrealizable specifications.