Data exchange, the problem of transferring data from a source schema to a target schema, has been studied for several years. The semantics of answering positive queries over the target schema has been defined in early work, but little attention has been paid to more general queries. A few proposals of semantics for more general queries exist but they either do not properly extend the standard semantics under positive queries, giving rise to counterintuitive answers, or they make query answering undecidable even for the most important data exchange settings, for example, with weakly-acyclic dependencies.

The goal of this paper is to provide a new semantics for data exchange that is able to deal with general queries. At the same time, we want our semantics to coincide with the classical one when focusing on positive queries, and to not trade-off too much in terms of complexity of query answering. We show that query answering is undecidable in general under the new semantics, but it is $\text{co}\text{NP}\text{-complete}$ when the dependencies are weakly-acyclic. Moreover, in the latter case, we show that exact answers under our semantics can be computed by means of logic programs with choice, thus exploiting existing efficient systems. For more efficient computations, we also show that our semantics allows for the construction of a representative target instance, similar in spirit to a universal solution, that can be exploited for computing approximate answers in polynomial time.

Hewlett-Packard develops and markets a family of computer-aided engineering products used by high-frequency designers to model the signal path in contemporary communications systems. As design frequencies, clock speeds and packaging densities continue to increase, more designers are finding that system and circuit simulation products need to be complemented by electromagnetic simulation software to develop models for basic circuit functionality or to characterize and compensate undesired parasitic effects. The HP High-Frequency Structure Simulator (HP HFSS) is a frequency-domain, finite element-based simulator, which enables engineers to characterize high-frequency behavior in 2D (transmission lines) and arbitrary 3D structures. Links with mechanical computer aided design (CAD) software have also become more important as the 3D structures to be analyzed by HP HFSS can involve packaging parasitics when the housing in which the electrical circuitry is enclosed becomes an influence on the signal path. Depending upon the complexity of the structure to be analyzed, HP HFSS can require hundreds of Mbytes of RAM and disk during automated adaptive solution convergence processes which determine field and circuit parameter solution results to user-specified accuracies. Although computer resource requirements will always be an important consideration for users of this type of product, another important situation to address for the future involves the exchange of data between the different simulation and modelling tools required to take design from concept through simulation to manufacture. The introduction of physical simulation tools into the traditional circuit simulation arena changes the design process flow and increases the demand for improved integration and interoperability of circuit simulators, numerical EM simulators, and mechanical CAD software. This paper provides an overview of data exchange issues in high-frequency electrical–physical–mechanical design processes.