Querying Fuzzy Description Logics and Ontology Knowledge Bases

Abstract

In order to represent the widespread imprecision and uncertainty in Semantic Web applications, there have been substantial amounts of work carried out in the context of fuzzy extensions of (Description Logics) DLs and ontologies, and corresponding reasoning algorithms and reasoners are thus developed. Also, some querying techniques are developed to provide users with querying services. However, some existing simple queries, such as instance retrieval, are relatively weak in expressive power and are unable to effectively express users’ query intents. Therefore, with emergence of these large-scale fuzzy DL knowledge bases (KBs) and fuzzy ontologies, it is of particular importance to provide users with expressive querying services. In particular, conjunctive queries (CQs) originated from research in relational databases, and, more recently, have also been identified as a desirable form of querying DL knowledge bases. Conjunctive queries provide an expressive query language with capabilities that go beyond standard instance retrieval. In this chapter, we will focus on the querying techniques of fuzzy DL KBs and fuzzy ontologies. We aim at introducing the conjunctive querying techniques from tractable to more expressive fuzzy DL KBs. Also, querying over fuzzy ontologies and some flexible extensions to the W3C standard query language SPARQL will be included.