What to Ask to an Incomplete Semantic Web Reasoner?
Bernardo Cuenca Grau and Giorgos Stoilos
Largely motivated by Semantic Web applications, many highly scalable, but incomplete, query answering systems have been recently developed. Evaluating the scalability-completeness trade-off exhibited by such systems is an important requirement for many applications. In this paper, we address the problem of formally comparing complete and incomplete systems given an ontology schema (or TBox) T. In particular, we formulate precise conditions under which an incomplete system is indistinguishable from a complete one w.r.t. the given T, regardless of the user's query and input data. Our results also allow us to quantify the ``degree of incompleteness'' of a given system relative to T as well as to automatically identify concrete queries and data patterns for which the incomplete system will miss answers.