The language Hi(DL-LiteR) is obtained from DL-LiteR by adding meta-modeling 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 all metavariables in all possible ways. Even though 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 meta-variables 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.

Practical higher-order query answering over Hi(DL-LiteR) knowledge bases / Lenzerini, Maurizio; Lepore, Lorenzo; Poggi, Antonella. - STAMPA. - 1193:(2014), pp. 608-619. ((Intervento presentato al convegno 27th International Workshop on Description Logics, DL 2014 tenutosi a Vienna, Austria nel 17-20 July 2014.

Practical higher-order query answering over Hi(DL-LiteR) knowledge bases

LENZERINI, Maurizio;LEPORE, LORENZO;POGGI, Antonella
2014

Abstract

The language Hi(DL-LiteR) is obtained from DL-LiteR by adding meta-modeling 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 all metavariables in all possible ways. Even though 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 meta-variables 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.
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