Query Optimization Techniques Exploiting Class Hierarchies

Since the introduction of object base management systems (OBMS), many query optimization techniques tailored for object query languages have been proposed. They adapt known optimization techniques to the OBMS context, exploit special object-oriented features, or give solutions to problems specific to querying objects. Nonetheless, one of the most prominent features of object models --- namely class hierarchies --- have so far not been exploited for query optimization. The current paper proposes new optimization techniques for queries referring to classes integrated into a class hierarchy. The techniques are generic in the sense that we do not give a set of algebraic equivalences the optimizer has to apply, but instead try to provide the reader with a general understanding of how to exploit class hierarchies for query optimization purposes. We give general descriptions of the techniques as well as illustrating examples. Besides yielding considerable savings in terms of execution time, t..