Gautam Bhargava

Efficient processing of outer joins and aggregate junctions

Removal of redundant outer joins is essential for the reassociation of outer joins with other binary operations. We present a set of comprehensive algorithms that employ the properties of strong predicates along with the properties of aggregation, intersection, union, and except operations to remove redundant outer joins from a query. For the purpose of query simplification, we generate additional projections by determining the keys. Our algorithm for generating keys is based on a novel concept of weak bindings that is essential for queries containing outer joins. Our algorithm for converting outer joins to joins is based on a novel concept of join-reducibility.