Making Metaquerying Practical for Hi(DL-Lite R)-Knowledge Bases

Hi(DL-LiteR) is a higher-order Description Logic obtained from DL-LiteR by adding metamodeling features, and is equipped with a query language that is able to express higher-order queries. We investigate the problem of answering a particular class of such queries, called instance higher-order queries, posed over Hi(DL-LiteR) knowledge bases (KBs). The only existing algorithm for this problem is based on the idea of reducing the evaluation of a higher- order query q over a Hi(DL-LiteR) KB to the evaluation of a union of first-order queries over a DL-LiteR KB, built from q by instantiating its metavariables in all possible ways. Although of polynomial time complexity with respect to the size of the KB, this algorithm turns out to be inefficient in practice. In this paper we present a new algorithm, called Smart Binding Planner (SBP), that compiles Q into a program, that issues a sequence of first-order conjunctive queries, where each query has the goal of providing the bindings for metavariables of the next ones, and the last one completes the process by computing the answers to Q. We also illustrate some experiments showing that, in practice, SBP is significantly more efficient than the previous approach.