Some recently proposed extensions to relational database systems, as well as to deductive database systems, require support for multiple-query processing. For example, in a database system enhanced with inference capabilities, a simple query involving a rule with multiple definitions may expand to more than one actual query that has to be run over the database. It is an interesting problem then to come up with algorithms that process these queries together instead of one query at a time. The main motivation for performing such an interquery optimization lies in the fact that queries may share common data. We examine the problem of multiple-query optimization in this paper. The first major contribution of the paper is a systematic look at the problem, along with the presentation and analysis of algorithms that can be used for multiple-query optimization. The second contribution lies in the presentation of experimental results. Our results show that using multiple-query processing algorithms may reduce execution cost considerably.

Abstract-Datalog is a database query language based on the logic programming paradigm; it has been designed and intensively studied over the last five years. We present the syntax and semantics of Datalog and its use for querying a relational database. Then, we classify optimization methods for achieving efficient evaluations of Datalog queries, and present the most relevant methods. Finally, we discuss various exhancements of Datalog, currently under study, and indicate what is still needed in order to extend Datalog’s applicability to the solution of real-life problems. The aim of this paper is to provide a survey of research performed on Datalog, also addressed to those members of the database community who are not too familiar with logic programming concepts. Zndex Terms-Deductive databases, logic programming, recursive queries, relational databases, query optimization. I.

Databases and information systems are often hard to use because they do not explicitly attempt to cooperate with their users. Direct answers to database and knowledge base queries may not always be the best answers. Instead, an answer with extra or alternative information may be more useful and less misleading to a user. This paper surveys foundational work that has been done toward endowing intelligent information systems with the ability to exhibit cooperative behavior. Grice's maxims of cooperative conversation, which provided a starting point for the field of cooperative answering, are presented along with relevant work in natural language dialogue systems, database query answering systems, and logic programming and deductive databases. The paper gives a detailed account of cooperative techniques that have been developed for considering users' beliefs and expecations, presuppositions, and misconceptions. Also, work in intensional answering and generalizing queries and answers is co...

this paper. Similarly, we have shown that integrity constraints can apply to temporal conditions, but that there is no one uniform approach to handling temporal databases. Many areas of the use of integrity constraints still need investigating. Below, we discuss some aspects associated with this topic that require additional work. ffl Implement semantic query optimization and cooperative answering systems. Current relational and deductive database systems do not provide these capabilities, but the current 30 April 1997 ICs: Semantics and Applications---Godfrey, Grant, Gryz, & Minker p. 36 of 46 standards for SQL provide for the incorporation of some aspects of integrity constraints.

. Database systems can be difficult to use. Part of the problem is that systems do not, for the most part, help a user when a query fails or fails to evaluate as the user expects. Schema and semantics of databases are often complex, and are rarely understood in entirety by the lay user. As a consequence, queries a lay user casts may not make sense with respect to a database's semantics. A system which returns informative responses beyond a query's answer set itself can elucidate the schema and semantics of the database, which can greatly help the user to cast the queries intended. Such a database system is to be called a cooperative database system (CDBS). A number of cooperative behaviors and methods have been introduced to be incorporated into information systems to make them more informative and, hence, easier to use. We have identified a fundamental set of such cooperative techniques that we believe relational and deductive systems should be extended to include. We present an archi...

Semantic query optimization uses problem-specific knowledge, represented as semantic constraints, to answer queries efficiently. Although the potential cost savings from semantic query optimization have been amply demonstrated, so far few cheap and effective search strategy for an optimal set of query transformations have been reported. This paper is based on our experience in designing and implementing a prototype semantic query optimizer for an object-oriented database system. Our approach tentatively applies all the possible transformations and delays the choice of beneficial transformations till the end. This approach makes the order of transformations immaterial and makes it possible to have an algorithm for query transformations that is of polynomial complexity. Preliminary experiments on the prototype show that the optimizer performs well for large databases. 1.

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Conjunctions of inequality predicates, or inequalities for short, have been utilized to represent conjunctive queries and semantic integrity constraints in semantic query processing systems (Klug 1988, Ullman 1989, Shenoy and Ozsoyoglu 1989, Guo et al. 1996). In conjunctive query containment problem, one needs to check whether a conjunction or set of inequality predicates implies an inequality. This test is also applicable to checking redundant inequalities in an integrity constraint represented by a conjunction or to checking the satisfiability of a constraint. Ullman (1989) presents 8 axioms that calculate the transitive closure of a set of inequalities to check whether an inequality is implied by a conjunction or set of inequalities. The closure algorithm does not directly handle equality (or inequalities that imply equalities) predicates and constants in inequalities. In this paper, we extend the Ullman's closure algorithm by allowing constants and equalities (or rather inequalitie...

We present a technique for semantic query optimization (SQO) for object databases. We use the ODMG standard languages ODL and OQL. The object schema and object query are translated into a Datalog representation. Semantic knowledge about the object model and the particular application is expressed as integrity constraints. SQO is performed in the Datalog representation and an equivalent logic query, and subsequently an equivalent object query, is obtained. SQO is based on the residue technique of [4]. We show that our technique generalizes previous research on SQO for object databases. It can also be applied to queries with methods and structure constructors and it can utilize access support relations. 1 Introduction In this paper we show how to apply semantic query optimization (SQO) techniques to query processing in object databases. SQO uses semantic knowledge in the form of integrity constraints (ICs) to reformulate an object query into an equivalent form that can be evalu...

Databases and information systems are often hard to use because they do not explicitly attempt to cooperate with their users. Direct answers to database and knowledge base queries may not always be the best answers. Instead, an answer with extra or alternative information may be more useful and less misleading to a user. This paper surveys foundational work that has been done toward endowing intelligent information systems with the ability to exhibit cooperative behavior. Grice's maxims of cooperative conversation, which provided a starting point for the field of cooperative answering, are presented along with relevant work in natural language dialogue systems, database query answering systems, and logic programming and deductive databases. The paper gives a detailed account of cooperative techniques that have been developed for considering users' beliefs and expecations, presuppositions, and misconceptions. Also, work in intensional answering and generalizing queries and answers is c...