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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 ooers a data model and a common query language that are designed to support the combining of information from many diierent sources. It also ooers tools for generating automatically the components that are needed to build systems for integrating(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)
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)
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)
When integrating heterogeneous information resources , it is often the case that the source is rather limited in the kinds of queries it can answer. If a query is asked of the entire system, we h a ve a new kind of optimization problem, in which w e m ust try to express the given query in terms of the limited query templates that this source can answer. For(More)
Semistructured data has no absolute schema xed in advance and its structure may be irregular or incomplete. Such data commonly arises in sources that do not impose a rigid structure such a s the WorldWide Web and when data is combined from several heterogeneous sources. Data models and query languages designed for well structured data are inappropriate in(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)