Héctor J. Hernández

Structural query optimization—a uniform framework for semantic query optimization in deductive databases

Recursion is at once a source of increased expressive power and high complexity for query languages like Datalog. A major question therefore is efficient processing of recursive queries. The first line of attack to process a recursive Datalog program P is to try to see if we can remove its recursivity; this is equivalent to testing whether there is a nonrecursive Datalog program which is equivalent to P. If this is the case, then P is said to be bounded [CGKV, GMSV, I, Nl, NS]. In general, the problem of testing whether a Datalog program is bounded is known to be undecidable even for linear programs with one idb predicate [GMSV]. Some other decidable and undecidable results on boundedness of Datalog programs are presented in [A, CGKV, K, Nl, NS, S, Var]. For a detailed summary of the present state-of-the-art of this problem see [KA]. None of the positive results above take into account the integrity constraints that may be satisfied by the predicates in the program.

Independence-reducible database schemes

A generahzatlon of Sagiv-independent database schemes, called (key-equivalent) independence-reducible schemes, is defined, and it is shown that it 1s highly desirable with respect to query answering and constraint enforcement. By showing that they are bounded and algebraic-maintamable the desirabdlties are proven. The class of independence-reducible schemes M exactly the class of schemes obtained from decomposing relation schemes in a Sagwmdependent scheme in a dependency preserving manner. Todemonstrate theclass ofschemes identified is rather general. itisprovedthatlt contains all prewously known classes of dependency preserving BCNF database schemes with similar properties. An efficient algorlthm is found which recognizes exactly this class of database schemes. Independence-reducible database schemes contain a class of constant-time-maintamable database schemes. A condition is found which characterizes this class of schemes and the condition can be tested efficiently. Throughout, it is assumed that a cover of the functional dependencies is embedded m a database scheme in the form of key dependencies.

Testing bag-containment of conjunctive queries

Abstract. Under the bag-theoretic semantics relations are bags of tuples, that is, a tuple may have any number of duplicates. Under this semantics, a conjunctive query

Constant-time-maintainable BCNF database schemes

Q

Containment of Conjunctive Queries with Built-in Predicates with Variables and Constants over any Ordered Domain

is bag-contained in a conjunctive query

The Chase of Datalog Programs

Q^{\prime }

Extended nested relations

, denoted

A network surveillance protocol for distributed database systems

Q\leq _bQ^{\prime }

A simple proof on the decidability of equivalence between recursive and nonrecursive Datalog programs

, if for all databases

Chasing Programs in Datalog.

{\cal D}