On the decidability of query containment under constraints

Diego Calvanese, Giuseppe De Giacomo, Maurizio Lenzerini
1998 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems - PODS '98  
Query containment under constraints is the problem of checking whether for every database satisfying a given set of constraints, the result of one query is a subset of the result of another query. Recent research points out that this is a central problem in several database applications, and we address it within a setting where constraints are speci ed in the form of special inclusion dependencies over complex expressions, built by using intersection and di erence of relations, special forms of
more » ... quanti cation, regular expressions over binary relations, and cardinality constraints. These types of constraints capture a great variety of data models, including the relational, the entity-relational, and the object-oriented model. We study the problem of checking whether q is contained in q 0 with respect to the constraints speci ed in a schema S, where q and q 0 are nonrecursive Datalog programs whose atoms are complex expressions. We present the following results on query containment. For the case where q does not contain regular expressions, we provide a method for deciding query containment, and analyze its computational complexity. W e do the same for the case where neither S nor q, q 0 contain number restrictions. To the best of our knowledge, this yields the rst decidability result on containment of conjunctive queries with regular expressions. Finally, w e prove that the problem is undecidable for the case where we admit inequalities in q 0 .
doi:10.1145/275487.275504 dblp:conf/pods/CalvaneseGL98 fatcat:gii3q6zdtfheplwoo35zd5xot4