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In this paper, we address the issue of reasoning with two classes of commonly used semantic integrity constraints in database and knowledge{base systems: implication constraints and referential constraints. We rst consider a central problem in this respect, the IRC{refuting problem, which is to decide whether a conjunctive query always produces an empty(More)
The control of organ growth is a fundamental aspect of animal development but remains poorly understood. The morphogen Dpp has long been considered as a general promoter of cell proliferation during Drosophila wing development. It is an ongoing debate whether the Dpp gradient is required for the uniform cell proliferation observed in the wing imaginal disc.(More)
The containment and minimization of conjunctive queries are two basic problems of query optimization in relational and deductive databases. For equality queries, the problems are NP{complete due to the \homomorphism property". For (in)equality queries, however, the containment problem has recently been proved to be p 2 {complete ((12]), while the(More)
In this paper, we address the complexity issue of reasoning with implication constraints. We consider the IC-RFT problem, which is the problem of deciding whether a conjunctive yes/no query always produces the empty relation (\no" answer) on database instances satisfying a given set of implication constraints, as a central problem in this respect. We show(More)
Drop-shipping has provided traditional retailers a new means with which to fulfill orders. Consequently, many traditional suppliers have offered dual-channel (traditional and drop-shipping channel) to retailers. Despite the increasing prevalence of this practice, several fundamental questions remain for suppliers: (1) Does it pay off to offer drop-shipping(More)