SQL4X: A Flexible Query Language for XML and Relational Databases (original) (raw)
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Proceedings of the 2003 ACM symposium on Applied computing - SAC '03, 2003
This paper proposes a way to integrate cleanly relational databases and XML documents. The main idea is to draw a clear line of demarcation between the two concepts by modelling XML documents as a new atomic SQL type. The standardised XML tools like XPath, XQuery, XSLT are then user-defined functions that operate on this type. Welldefined interoperability is guaranteed by, on the one hand, defining a standard way to markup SQL relations as XML documents and, thus, to make them accessible to the XML tools; on the other hand, XPath and XQuery queries run against the XML portion of the database can use the same predefined schema to make their results accessible to the SQL language for further processing. Additionally, a method for set-oriented evaluation of regular path expressions is presented that integrates into our implementation framework.
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An important application of XML is the interchange of electronic data (EDI) between multiple data sources on the Web. As XML data proliferates on the Web, applications will need to integrate and aggregate data from multiple source and clean and transform data to facilitate exchange. Data extraction, conversion, transformation, and integration are all well-understood database problems, and their solutions rely on a query language. We present a query language for XML, called XML-QL, which we argue is suitable for performing the above tasks. XML-QL is a declarative, 'relational complete' query language and is simple enough that it can be optimized. XML-QL can extract data from existing XML documents and construct new XML documents.
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The proposed approach to XML query formulation and evaluation developed by means of XML Declamtive Description (XDD) theory formalizes a query as an XDD description comprising one or more XML clauses the syntax of which can be subdivided into the three specifications: pattern of XML elements to be selected, the query's selection criteria and the structure of the resulting elements. It supports formulation of essential functionality requirements for an XML query language such as selection and extraction, combination, transformation, closure and nested queries. Evaluation of a query on a specified XML database is carried out by employment of Equivalent 'I'ransformation paradigm. Moreover, since XDD theory provides a simple mechanism for representation of knowledge and relationships among elements in a The original version of this chapter was revised: The copyright line was incorrect. This has been corrected. The Erratum to this chapter is available at
1998
A query language is essential, if XML is to serve e ectively as an exchange medium for large data sets. The design of query languages for XML is in its infancy, and the choice of a standard may be governed more by user acceptance than by any understanding of underlying principles. One would hope that expressive power, performance, and compatibility with other languages will be considered in choosing among alternatives, but it is likely that several contenders will co-exist for some time.
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Proceedings of the Third International Conference on Web Information Systems Engineering, 2002. WISE 2002., 2002
A semantic query attempts to help a user to obtain or manipulate data in a database without knowing its detailed syntactic structure. Formulation and evaluation of semantic queries require schematic and other constraint information as well as general domain knowledge. A new approach to the formulation and evaluation of semantic queries for XML databases is proposed. It employs XML Declarative Description (XDD)-an XML based knowledge representation-to model the databases together with the schemata of their XML elements and to represent domain knowledge resulting in a uniform representation of all the required information. Equivalent Transformation (ET)-a new computation paradigm which transform a representation into another one while preserving their meanings-is used to optimize and evaluate the queries.
A general technique for querying XML documents using a relational database system
ACM SIGMOD …, 2001
There has been recent interest in using relational database systems to store and query XML documents. Each of the techniques proposed in this context works by (a) creating tables for the purpose of storing XML documents (also called relational schema generation), (b) storing XML documents by shredding them into rows in the created tables, and (c) converting queries over XML documents into SQL queries over the created tables. Since relational schema generation is a physical database design issue -dependent on factors such as the nature of the data, the query workload and availability of schemas -there have been many techniques proposed for this purpose. Currently, each relational schema generation technique requires its own query processor to efficiently convert queries over XML documents into SQL queries over the created tables. In this paper, we present an efficient technique whereby the same query-processor can be used for all such relational schema generation techniques. This greatly simplifies the task of relational schema generation by eliminating the need to write a special-purpose query processor for each new solution to the problem. In addition, our proposed technique enables users to query seamlessly across relational data and XML documents. This provides users with unified access to both relational and XML data without them having to deal with separate databases. SIGMOD
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