Compact representation for answer sets of n-ary regular queries

An n-ary query over trees takes an input tree t and returns a set of n-tuples of the nodes of t. In this paper, a compact data structure is introduced for representing the answer sets of n-ary queries defined by tree automata. Despite that the number of the elements of the answer set can be as large as |t|n, our representation allows storing the set using only O(|t|) space. Several basic operations on the sets are shown to be efficiently executable on the representation.