Evaluation and optimization of complex object selections

We provide a general framework for declarative selection operations for complex object databases based on the safe calculus for complex objects Within this framework we consider a class of single pass evaluable selection operations We show how such selection operations can be succinctly expressed by programs that use only very simple positive existential selections Also a syntactic criterion is developed for the commutation of two such positive existential selections These two results are then jointly applied to the problem of optimizing complex object selections which is much more complicated than in classical relational databases