Closing the Gap Between XML and Relational Database Technologies: State-of-the-Practice, State-of-the-Art and Future Directions

Closing the Gap Between XML and Relational Database Technologies: State-of-the-Practice, State-of-the-Art and Future Directions

Mary Ann Malloy (The MITRE Corporation, USA) and Irena Mlynkova (Charles University, Czech Republic)
DOI: 10.4018/978-1-60566-308-1.ch001
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As XML technologies have become a standard for data representation, it is inevitable to propose and implement efficient techniques for managing XML data. A natural alternative is to exploit tools and functions offered by relational database systems. Unfortunately, this approach has many detractors, especially due to inefficiency caused by structural differences between XML data and relations. But, on the other hand, relational databases represent a mature, verified and reliable technology for managing any kind of data including XML documents. In this chapter, the authors provide an overview and classification of existing approaches to XML data management in relational databases. They view the problem from both state-of-the-practice and state-of-the-art perspectives. The authors describe the current best known solutions, their advantages and disadvantages. Finally, they discuss some open issues and their possible solutions.
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Without a doubt, the extensible markup language (XML) (Bray et al., 2006) is one of the most popular contemporary formats for data representation. It is well-defined, easy-to-use and involves various recommendations such as languages for structural specification, transformation, querying, updating, etc. This wide popularity naturally has evoked intense effort to propose faster and more efficient methods and tools for managing and processing XML data. Soon it became possible to distinguish several different directions. The four most popular approaches are: methods that store XML data in a classical file system; methods that store and process XML data using a relational database system; methods that exploit a pure object-oriented approach; and, native XML methods that use special indices, numbering schemes and/or data structures particularly suitable for the tree structure of XML data. Naturally, each of these approaches has both keen advocates and detractors who emphasize its particular advantages or disadvantages.

The situation is not good especially for file system-based and pure object-oriented methods. The former approach suffers from an inability to query without any additional pre-processing of the data; whereas the latter approach fails in particular in finding a corresponding efficient and comprehensive implementation. As expected, the highest-performance techniques are the native ones, since they are tailored particularly for XML processing and do not need to artificially adapt existing structures to a new purpose. Nevertheless, the most practically used methods exploit features of relational databases. Although researchers have already proven that native XML strategies perform much better, they still lack one important aspect: a robust implementation verified by years of both theoretical and practical effort.

If we consider this problem from an alternative viewpoint, we realize that considerable amounts of data in practical use are still stored in relational databases. Legacy relational stores are well-established and reliable enough that their existence is entrenched and they are unlikely to disappear anytime soon (Bruce, 2007). Developers must sustain existing investments in applications predicated on a relational architecture while, at the same time, adapting them to the heterogeneous and message-driven nature of XML. A typical use case may involve mapping Web document content from an XML representation into a relational database. Not only does this help insulate naïve Web clients from the underlying and perhaps less familiar XML technologies, it also positions the information for storage and query via the more mature technologies associated with RDBMSs. Alternatively, middleware may permit XML sophisticates to view and query relational contents as though they were XML documents, and vice versa. For the foreseeable future, some hybrid of these solutions is likely to be developed, although the major relational database vendors are already providing embedded XML support.

Consequently, currently there are many efforts focused on database-centric XML data management. The researchers focus on more efficient strategies to query evaluation, database vendors more and more support XML and even the SQL standard has been extended by SQL/XML which introduces a new XML data type and operations for XML data manipulation. But, although the amount of existing solutions is large, there are still unsolved problems, open issues and aspects to be improved.

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Table of Contents
Ernesto Damiani
Eric Pardede
Eric Pardede
Chapter 1
Mary Ann Malloy, Irena Mlynkova
As XML technologies have become a standard for data representation, it is inevitable to propose and implement efficient techniques for managing XML... Sample PDF
Closing the Gap Between XML and Relational Database Technologies: State-of-the-Practice, State-of-the-Art and Future Directions
Chapter 2
Mirella M. Moro, Lipyeow Lim, Yuan-Chi Chang
It is well known that XML has been widely adopted for its flexible and self-describing nature. However, relational data will continue to co-exist... Sample PDF
Challenges on Modeling Hybrid XML-Relational Databases
Chapter 3
Vassiliki Koutsonikola, Athena Vakali
Nowadays, XML has become the standard for representing and exchanging data over the Web and several approaches have been proposed for efficiently... Sample PDF
XML and LDAP Integration: Issues and Trends
Chapter 4
Giovanna Guerrini, Marco Mesiti
The large dynamicity of XML documents on the Web has created the need to adequately support structural changes and to account for the possibility of... Sample PDF
XML Schema Evolution and Versioning: Current Approaches and Future Trends
Chapter 5
Mingzhu Wei, Ming Li, Elke A. Rundensteiner, Murali Mani, Hong Su
Stream applications bring the challenge of efficiently processing queries on sequentially accessible XML data streams. In this chapter, the authors... Sample PDF
XML Stream Query Processing: Current Technologies and Open Challenges
Chapter 6
Sven Groppe, Jinghua Groppe, Christoph Reinke, Nils Hoeller, Volker Linnemann
The widespread usage of XML in the last few years has resulted in the development of a number of XML query languages like XSLT or the later... Sample PDF
XSLT: Common Issues with XQuery and Special Issues of XSLT
Chapter 7
Mirella M. Moro, Zografoula Vagena, Vassilis J. Tsotras
Content-based routing is a form of data delivery whereby the flow of messages is driven by their content rather than the IP address of their... Sample PDF
Recent Advances and Challenges in XML Document Routing
Chapter 8
Philippe Poulard
XML engines are usually designed to solve a single class of problems: transformations of XML structures, validations of XML instances, Web... Sample PDF
Native XML Programming: Make Your Tags Active
Chapter 9
Stéphane Bressan, Wee Hyong Tok, Xue Zhao
Since XML technologies have become a standard for data representation, a great amount of discussion has been generated by the persisting open issues... Sample PDF
Continuous and Progressive XML Query Processing and its Applications
Chapter 10
Fabio Grandi, Federica Mandreoli, Riccardo Martoglia
In several application fields including legal and medical domains, XML documents are “versioned” along different dimensions of interest, whose... Sample PDF
Issues in Personalized Access to Multi-Version XML Documents
Chapter 11
Tran Khanh Dang
In an outsourced XML database service model, organizations rely upon the premises of external service providers for the storage and retrieval... Sample PDF
Security Issues in Outsourced XML Databases
Chapter 12
Marco Mesiti, Ernesto Jiménez Ruiz, Ismael Sanz, Rafael Berlanga Llavori, Giorgio Valentini, Paolo Perlasca, David Manset
There is a proliferation of research and industrial organizations that produce sources of huge amounts of biological data issuing from... Sample PDF
Data Integration Issues and Opportunities in Biological XML Data Management
Chapter 13
Doulkifli Boukraa, Riadh Ben Messaoud, Omar Boussaid
Current data warehouses deal for the most part with numerical data. However, decision makers need to analyze data presented in all formats which one... Sample PDF
Modeling XML Warehouses for Complex Data: The New Issues
Chapter 14
Irena Mlynkova
Since XML technologies have become a standard for data representation, numerous methods for processing XML data emerge every day. Consequently, it... Sample PDF
XML Benchmarking: The State of the Art and Possible Enhancements
About the Contributors