Implementing Generalized Transitive Closure in the Paradise Geographical Information System
نویسنده
چکیده
The generalized transitive closure operator can be used to ask and answer a number of sophisticated queries on a database which is viewed as a directed graph. These queries cannot be expressed in SQL or relational algebra and neither can they be answered by commercially available relational or object-oriented database systems. In this report we describe the design and implementation of the generalized transitive closure operator in Paradise, an experimental geographical information system, a domain in which this operator is especially useful. We show how semi-naive evaluation, a basic technique for evaluating recursive queries, can be extended to compute aggregates and we also give a formal proof of the correctness of our method. We also discuss how selections can be used to optimize the evaluation of the query. The report concludes with a few examples of how these queries can now be expressed in the extended SQL like query language of Paradise and what the results look like.
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