Weight-based consistent query answering over inconsistent \({\mathcal {SHIQ}}\) knowledge bases

摘要

Non-standard query mechanisms that work under inconsistency are required in some important description logic (DL)-based applications, including those involving an inconsistent DL knowledge base ( KB) whose intensional knowledge is consistent but is violated by its extensional knowledge. This paper proposes a weight-based semantics for querying such an inconsistent KB. This semantics defines an answer of a conjunctive query posed upon an inconsistent KB as a tuple of individuals whose substitution for the variables in the query head makes the query body entailed by any subbase of the KB consisting of the intensional knowledge and a weight-maximally consistent subset of the extensional knowledge. A novel computational method for this semantics is proposed, which works for extensionally reduced \({\mathcal {SHIQ}}\) KBs and conjunctive queries without non-distinguished variables. The method first compiles the given KB to a propositional program; then, for any given conjunctive query, it reduces the problem of computing all answers of the given query to a set of propositional satisfiability (SAT) problems with PB-constraints, which are then solved by SAT solvers. A decomposition-based framework for optimizing the method is also proposed. The feasibility of this method is demonstrated in our experiments.