Information systems typically support only a limited set of queries over the schema they export. The reason is that the participating information sources contribute limited content and limited access methods. We describe the CLIDE interactive system, which extends the QBE-like query builder of Microsoft's SQL Server with a coloring scheme that guides the user toward formulating feasible queries. We formalize the behavior of the system using an interaction graph. We present a modular architecture consisting of a front-end and a back-end that enables the front-end's behavior by providing answers to particular questions about the interaction graph. We developed a back-end for the case where the content and the access methods are described using parameterized views, a formalism that has been used in integration architectures. In this case the set of feasible queries consists of the queries that have an equivalent rewriting using the views. We present the algorithms, implementation and performance of the back-end, showing that CLIDE is a viable online tool.
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