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In a data exchange system the correctness of the system depends on data exchange semantics. This can be well verified by using query answering. In the close world assumption (CWA) two types of answers are obtained, one is certain answer, which ignores the null values, another is maybe answer, which considers the null values. In this thesis, we give a procedure for computing a finite representation...
Today XML is the de facto standard of data exchange format for the information on the Web. At the same time, database systems are well known for consistent storage, retrieval and manipulation of data. XML querying language (XPath) is used to access XML documents whereas Structured Query Language (SQL) for retrieving and manipulating data in relational database. It may not be possible for users and...
The accuracy and completeness of data exchange largely depend on the semantics of the data exchange problem and are best verified by answering queries over target instances in such a way that is semantically consistent with the source data. The concept of certain answers is used in the definition of the semantics of answering queries. But as certain answers are defined as a relation without null values,...
Extensible Markup Language (XML) has become an important format for data exchange and representation on the Web. In addition to conventional query processing, more complex analysis on XML data is considered to become important in order to discover valuable information. In this research, we attempt to investigate an XML-OLAP, by which we can perform multidimensional analysis on XML data taking XML's...
We study the problem of answering queries through a target RDF ontology, given a set of view-based mappings between one or more source relational schemas and this target ontology. We design a novel query rewriting algorithm that can efficiently rewrites a RDF query into relational queries using a set of RDF views. With our approach, we highlight the important role played by RDF blank node in representing...
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