Mapping-equivalence and oid-equivalence of single-function object-creating conjunctive queries
Van den Bussche J
MetadataShow full item record
Conjunctive database queries have been extended with a mechanism for object creation to capture important applications such as data exchange, data integration, and ontology-based data access. Object creation generates new object identifiers in the result that do not belong to the set of constants in the source database. The new object identi- fiers can be also seen as Skolem terms. Hence, object-creating conjunctive queries can also be regarded as restricted second- order tuple-generating dependencies (SO-tgds), considered in the data exchange literature. In this paper, we focus on the class of single-function object-creating conjunctive queries, or sifo CQs for short. The single-function symbol can be used only once in the head of the query. We give a new character- ization for oid-equivalence of sifo CQs that is simpler than the one given by Hull and Yoshikawa and places the prob- lem in the complexity class NP. Our characterization is based on Cohen’s equivalence notions for conjunctive queries with multiplicities. We also solve the logical entailment problem for sifo CQs, showing that also this problem belongs to NP. Results by Pichler et al. have shown that logical equivalence for more general classes of SO-tgds is either undecidable or decidable with as yet unknown complexity upper bounds.
Showing items related by title, author, creator and subject.
Cohen, S; Nutt, W; Sagiv, Y (Association for Computing Machinery, 2007)Equivalence of aggregate queries is investigated for the class of conjunctive queries with comparisons and the aggregate operators count, count-distinct, min, max, and sum. Essentially, this class contains unnested SQL ...
Hamel, AH (Elsevier, 2005)A minimal element theorem on sequentially complete uniform spaces is presented that generalizes earlier results of [Pacific J. Math. 55(2) (1974) 335–341; Proc. Amer. Math. Soc. 108(3) (1990) 707–714]. Two more equivalent ...
Cohen, S; Nutt, W; Sagiv, Y (Association for Computing Machinery (ACM), 2005)Query equivalence is investigated for disjunctive aggregate queries with negated subgoals, constants and comparisons. A full characterization of equivalence is given for the aggregation functions count, max, sum, prod, ...