The learnability of symbolic automata

Abstract

Symbolic automata (s-FAs) allow transitions to carry predicates over rich alphabet theories, such as linear arithmetic, and therefore extend classic automata to operate over infinite alphabets, such as the set of rational numbers. In this paper, we study the problem of the learnability of symbolic automata. First, we present M AT∗, a novel L∗ -style algorithm for learning symbolic automata using membership and equivalence queries, which treats the predicates appearing on transitions as their own learnable entities. The main novelty of M AT∗ is that it can take as input an algorithm Λ for learning predicates in the underlying alphabet theory and it uses Λ to infer the predicates appearing on the transitions in the target automaton. Using this idea, M AT∗ is able to learn automata operating over alphabets theories in which predicates are efficiently learnable using membership and equivalence queries. Furthermore, we prove that a necessary condition for efficient learnability of an s-FA is that predicates in the underlying algebra are also efficiently learnable using queries and thus settling the learnability of a large class of s-FA instances. We implement M AT∗ in an open-source library and show that it can efficiently learn automata that cannot be learned using existing algorithms and significantly outperforms existing automata learning algorithms over large alphabets.