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The problem of satisfiability of a specific class of integrity constraints in data bases, namely the dependency constraints, is analysed. An Entity-Relationship model is used for expressing data schemata. In this model suitable types of dependency constraints, called cardinality ratio constraints, allow one to impose restrictions on the mappings between(More)
We present a new Lagrangian-based heuristic for solving large-scale set-covering problems arising from crew-scheduling at the Italian Railways (Fer-rovie dello Stato). Our heuristic obtained impressive results when compared to state of the art codes on a test-bed provided by the company, which includes instances with sizes ranging from 50,000 variables and(More)
In this paper we deal with the Minimum Power Multicasting problem (MPM) in wireless ad-hoc networks. By using an appropriate choice of the decision variables and by exploiting the topological properties of the problem, we are able to define an original formulation based on a Set Covering model. Moreover, we propose for its solution two exact procedures that(More)
1 Abstract A (0; 1) matrix A is said to be ideal if all the vertices of the polytope Q(A) = fx : Ax 1; 0 x 1g are integral. The issue of nding a satisfactory characterization of those matrices which are minimally non-ideal is a well known open problem. An outstanding result toward the solution of this problem, due to Alfred Lehman, is the description of(More)