Query Unnesting in Object Oriented Database

Both relational and Object-oriented query languages allow nested queries (queries with subqueries). Nested queries are typically inefficient to execute in their original form and are difficult to optimize. Most existing query Unnesting techniques are based on source-to source, query graph, or calculus transformations. Few are based on algebraic transformations. Algebraic Unnesting is desirable for cost-based algebraic optimization, because it allows such optimizers to be more readily extended with Unnesting capabilities. This paper concentrates on a new algorithm for the execution of nested queries , which covers unnesting techniques for projection, predicate and range dependency which commonly occurs in OODBMS.