Title :
Default logic as a query language
Author :
Cadoli, Marco ; Eiter, Thomas ; Gottlob, Georg
Author_Institution :
Dipartimento di Inf. e Sistemistica, Rome Univ., Italy
Abstract :
Research in nonmonotonic reasoning has focused largely on the idea of representing knowledge about the world via rules that are generally true but can be defeated. Even if relational databases are nowadays the main tool for storing very large sets of data, the approach of using nonmonotonic AI formalisms as relational database query languages has been investigated to a much smaller extent. In this work, we propose a novel application of Reiter´s default logic by introducing a default query language (DQL) for finite relational databases, which is based on default rules. The main result of this paper is that DQL is as expressive as SO∃∀ the existential-universal fragment of second-order logic. This result is not only of theoretical importance: We exhibit queries-which are useful in practice-that can be expressed with DQL and cannot with other query languages based on nonmonotonic logics such as DATALOG with negation under the stable model semantics. In particular, we show that DQL is well-suited for diagnostic reasoning
Keywords :
formal logic; nonmonotonic reasoning; query languages; relational databases; default logic; default query language; diagnostic reasoning; finite relational databases; nonmonotonic logics; nonmonotonic reasoning; query language; relational database query languages; second-order logic; stable model semantics; Artificial intelligence; Birds; Computational complexity; Database languages; Information retrieval; Knowledge representation; Logic; Nuclear magnetic resonance; Relational databases;
Journal_Title :
Knowledge and Data Engineering, IEEE Transactions on