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<p>Many recursive query processing applications are still poorly supported, partly because implementations of general recursive capabilities are inefficient and hard to understand for users, partly because the approaches do not integrate well with existing query languages. An extension is proposed of the database language SQL for the processing of recursive structures. The new constructs are integrated in the view definition mechanism of SQL. Therefore, users with knowledge of SQL can take advantage of the increased functionally without learning a new language. The construct is based on a generalization of transitive closure and is formally defined. Because of the importance of extreme value sections, special constructs are introduced for the selection of tuples with minimal or maximal values in some attributes. Applying these selections on recursively defined views constitutes nonlinear recursion. By the introduction of special constructs for these selections, dealing with general nonlinear recursion can be avoided.</p>
general transitive closure; recursive query processing applications; general recursive capabilities; existing query languages; database language SQL; recursive structures; view definition mechanism; extreme value sections; special constructs; tuples; maximal values; attributes; recursively defined views; nonlinear recursion; database management systems; information retrieval systems; query languages; standards

J. Eder, "Extending SQL with General Transitive Closure and Extreme Value Selections," in IEEE Transactions on Knowledge & Data Engineering, vol. 2, no. , pp. 381-390, 1990.
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