The focus is semantic query optimization in the presence of integrity constraints such as inclusion dependencies and context dependencies (CDs). The authors provide the motivation for the type of integrity constraints considered and for the work at large. They introduce CDs formally and illustrate their power in capturing semantics with an example. An inference mechanism is described for reasoning with these constraints. Sufficient conditions for testing redundancy of atoms in rules and rules in programs are described, and polynomial time algorithms are provided for detecting and eliminating such redundancies. The technique uniformly applies to recursive as well as nonrecursive queries. The approach is illustrated with examples. The discussion and examples are presented in terms of recursive rules only.<>