Optimization and evaluation of relational queries: conjunctive query optimization, optimization of queries involving union and difference operators, algorithms for performing joins. Limitations of relational algebra as a query language.
Fixed-point queries and Horn-clause queries. Optimization and evaluation of Horn-clause queries: filtering data flow method, magic set and generalized counting methods, clause and literal deletion problems. The boundedness problem, reducing the complexity of recursion, Duplicate clause removal.
Incorporating functions, sets and negations into Horn-clause queries.
J. D. Ullman.Principles of Database and Knowledge Base Systems, Vol I & II, Computer Science Press, 1988.