Data structures for symbolic multi-valued model-checking

Multi-valued logics can be effectively used to reason about incomplete and/or inconsistent systems, e.g. during early software requirements or as the systems evolve. In our earlier work we identified a useful family of multi-valued logics: those specified over finite distributive lattices where negation preserves involution, i.e., , , -/.0for every element of the logic. Model-checking over this family of logics allows not only to extend the domain of applicability of automated reasoning to new problems, but also to speed up some classical verification problems. Symbolic model-checking over multi-valued logics can be cast in terms of operations over multivalued sets: sets whose membership functions are multi-valued. In this paper we propose and empirically evaluate several choices for implementing multi-valued sets with decision diagrams. In particular, we describe two major approaches: (1) representing the multi-valued membership function canonically, using MDDs or ADDs; (2) representing multi-valued sets as a collection of classical sets, using a vector of either MBTDDs or BDDs. The naive implementation of (2) includes having a classical set for each value of the logic. We exploit a result of lattice theory to reduce the number of such sets that need to be represented. The major contribution of this paper is the evaluation of the different implementations of multivalued sets, done via a series of experiments and using several case studies.