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Abstract

The system, method, and program of this invention, referred to herein as nest elimination, performs query rewrite transformations, within a database management system (DBMS), for a certain class of object queries over views that involve derived nested sets. The nest elimination algorithm uses query rewriting to avoid computing these nested sets in certain common cases. For each quantifier in a query (if the quantifier is defined over a nested set that is a part of a view or if the quantifier is implemented by a subquery that projects a NEST aggregate) the following functions are performed: a) resetting an element to which a quantifier is bound in the database query to an argument of a nest aggregate function in a nest subquery of a view; b) adding a null testing predicate to the rewritten database query; c) adding quantifiers defined within the nest subquery to the rewritten database query; d) adding predicates from the nest subquery of the view to the rewritten database query; and e) rewriting each expression involving a quantifier over an instance into a path expression. The resulting rewritten query is then further processed by the DBMS such as through a query optimizer, etc. By avoiding nested set computations for a certain class of queries, the rewritten query can result in improved processing performance.

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First Claim