Derivatives of Tree Sets with Applications to Grammatical Inference

Tree automata generalize the notion of a finite automaton working on strings to that of a finite automaton operating on trees. Most results for finite automata have been extended to tree automata. In this paper we introduce tree derivatives which extend the concept of Brzozowski's string derivatives. We use tree derivatives for minimizing and characterizing tree automata. Tree derivatives are used as a basis of inference of tree automata from finite samples of trees. Our method compares tree derivative sets and infers a tree automaton based on the amount of overlap between the derivative sets. Several of the limitations present in the tree inference techniques by Brayer and Fu and Edwards, Gonzalez, and Thomason are not imposed by our algorithm.