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XSEarch, a semantic search engine for XML, is presented. XSEarch has a simple query language , suitable for a naive user. It returns semantically related document fragments that satisfy the user's query. Query answers are ranked using extended information-retrieval techniques and are generated in an order similar to the ranking. Advanced indexing techniques(More)
TSIMMIS—The Stanford-IBM Manager of Multiple Information Sources—is a system for integrating information. It offers a data model and a common query language that are designed to support the combining of information from many different sources. It also offers tools for generating automatically the components that are needed to build systems for integrating(More)
Several methods for implementing database queries expressed as logical rules are given and they are compared for efficiency. One method, called " magic sets, " is a general algorithm for rewriting logical rules so that they may be implemented bottom-UP (= forward chaining) in a way that cuts down on the irrelevant facts that are generated. The advantage of(More)
We consider the problem of computing answers to queries by using materialized views. Aside from its potential in optimizing query evaluation, the problem also arises in applications such as Global Information Systems, Mobile Computing and maintaining physical data independence. We consider the problem of nding a rewriting of a query that uses the(More)
We present a computation method---the chase---for testing implication of data dependencies by a set of data dependencies. The chase operates on tableaux similar to those of Aho, Sagiv, and Ullman. The chase includes previous tableau computation methods as special cases. By interpreting tableaux alternately as mappings or as templates for instances, we can(More)
Constraints are a valuable tool for managing information across multiple databases, as well as for general purposes of assuring data integrity. However, efficient implementation of constraint checking is difficult. In this paper we explore techniques for assuring constraint satisfaction without performing a complete evaluation of the constraints. We(More)
Queries in relational databases can be formulated in terms of relational expressions using the relational operations select, project, join, union, and difference The equivalence problem for these queries is studied with query optimization m mind It ts shown that testmg eqmvalence of relational expressions with the operators select, project, join, and union(More)