Translating OSQL queries into efficient set expressions
Efficient query processing is one of the key promises of database technology. With the evolution of supported data models—from relational via nested relational to object-oriented—the need for such efficiency has not diminished, and the general problem has increased in complexity.
In this paper, we present a heuristics-based, extensible algorithm for the translation of object-oriented query expressions in a variant of OSQL to an algebra extended with specialized join operators, designed for the task. We claim that the resulting algebraic expressions are cost-efficient.
Our approach builds on well-known optimization strategies for the relational model, but extends them to include relations and more arbitrary sets as values. We pay special attention to the most costly forms of OSQL queries, namely those with full subqueries in the SELECT- or WHERE-clause. The paper builds on earlier results [17, 18].
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