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Identifier uch.csd.msc//2006kondylakis
Title Quete: Επεξεργασία Επερωτήσεων σε Κατανεμημένες Βάσεις Δεδομένων
Alternative Title Quete: Query Processing in distributed database systems
Creator Kondylakis, Haridimos G
Abstract The exponential growth of the web and the extended use of database management systems has brought to the fore the seamless interconnection of diverse and large numbers of information sources. The main problem in such an environment is the heterogeneity between these different sources. Our essential proposal to resolve the issue of heterogeneity, is finding mappings across schemata and a global reference ontology, the terms of which are used for annotation and querying. By accepting ontology as a point of common reference, naming conflicts are eliminated and semantic conflicts are reduced. Our contribution is a system that provides an automatic and scalable approach to integrate and then query transparently multiple data sources. It maps automatically semantic queries to SQL and presents the results to the user. Database metadata, are independently captured into XML documents, which also store semantic names for schema elements to identify identical concepts across systems. The query system is capable of handling complex join constructs, and choosing the appropriate attributes, relations and join conditions to preserve user query semantics. Moreover, since joins across databases are most difficult to handle, two join algorithms were implemented in order to study the efficiency of such a system. The query engine extended to support and exploit horizontal and vertical distribution of database’s tables. Those extensions boost the whole system performance when the knowledge of such a distribution exists. Experiments showed that the system has an acceptable performance even in large databases.
Issue date 2006-04-01
Date available 2006-07-19
Collection   School/Department--School of Sciences and Engineering--Department of Computer Science--Post-graduate theses
  Type of Work--Post-graduate theses
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