Query languages for data exchange: beyond unions of conjunctive queries

The class of unions of conjunctive queries (UCQ) has been shown to be particularly well-behaved for data exchange; its certain answers can be computed in polynomial time (in terms of data complexity). However, this is not the only class with this property; the certain answers to any DATALOG program can also can be computed in polynomial time. The problem is that both UCQ and DATALOG do not allow negated atoms, as adding an unrestricted form of negation to these languages yields to intractability. In this paper, we propose a language called DATALOG C(=) that extends DATALOG with a restricted form of negation, and study some of its fundamental properties. In particular, we show that the certain answers to a DATALOG C(=) program can be computed in polynomial time (in terms of data complexity), and that every union of conjunctive queries with at most one inequality or negated relational atom per disjunct, can be efficiently rewritten as a DATALOG C(=) program in the context of data exchan...

• Type: Conference
• Year: 2009
• Where: ICDT
• Authors: Juan Reutter, Marcelo Arenas, Pablo Barceló
• Keywords: Conjunctive Queries, Database, DATALOG, ICDT 2009, Language Called Datalog