Guest Editorial

Guest Editorial The VLDB Journal (2002) 11: 273 / Digital Object Identifier (DOI) 10.1007/s00778-002-0082-9 Alon Y. Halevy University of Washington, Seattle, WA 98195, USA; e-mail: Published online: December 13, 2002 –  c Springer-Verlag 2002 In the past few years, XML data management has been one The next set of papers are inspired by novel applications of the main research areas for the database community. Ac- scenarios enabled by XML. Chien et al. discuss the manage- cordingly, we received twenty-five submissions to the special ment of multi-version XML documents, a problem that occurs issue, covering many aspects of managing XML data. The six more frequently in XML applications. They describe a set of papers appearing in this issue were selected after two rounds methods, based on novel techniques for clustering XML ele- of review, and represent the current breadth of research on ments, which enables efficient querying over multiple versions XML. of XML documents. The papers represent the shift of research emphasis in Chan et al. consider publish-subscribe systems where sub- the community in the last couple of years. Early XML work scriptions to data are described by XPath queries (the idea of focused on developing query languages, and techniques for using XML in publish/subscribe systems was first elaborated leveraging relational databases for storing XML and answer- in work by Altinel and Franklin on XFilter). The challenge ing queries over XML data. This early work had incredible im- is to efficiently determine which subscribers should receive pact: today, a committee of the World-Wide Web Consortium, a given XML document from the publisher. Their system is which includes several researchers from the database com- based on XTrie, a method for indexing large numbers of XPath munity, has already proposed XQuery, a standard language expressions. for XML. In parallel, most commercial database products al- Finally, the paper by Ives et al. describes a system for ready support some form of storage and querying of XML processing queries over XML data that is streaming from the data, leveraging their relational engines. network. In this context, it is impractical to first load the data The focus of the research community has shifted to devel- into a local store and then process queries. The key innova- oping techniques for supporting native XML query process- tions in this paper are the x-scan operator that applies regular ing, and to supporting the needs of novel types of applications path expressions to data that are streaming in, and an internal that arise in the context of XML. representation of tree-structured data that enables leveraging The first two papers in the issue describe complete systems traditional pipelined query processing techniques. I would like for native XML data management. Jagadish et al. describe the to thank Tamer Ozsu, our Editor-in-Chief, for personally han- Timber system, focusing on their novel algebra for manipu- dling the review process of this paper to avoid conflicts of lating sets of trees and the query evaluation and optimization interest. methods they employ in the system. The Natix System, de- In summary, I believe that the papers in this issue are an scribed in the paper by Fiebig et al., focuses on the storage excellent and high-caliber snapshot of the current work in our sub-system and how it supports efficient transaction manage- community. I would like to thank Peter Fankhauser for his ment and recovery. The paper by Amer-Yahia et al. considers assistance in the early stages of handling the special issue, a specific query optimization issue, namely the problem of and Tamer Ozsu for his support throughout. minimizing tree pattern query expressions. The paper shows Alon Y. Halevy that there exists a unique minimal tree pattern query, and they University of Washington, Seattle, WA 98195, USA show how to find the minimal query efficiently. The VLDB Journal Springer Journals

Guest Editorial

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Copyright © 2002 by Springer-Verlag Berlin Heidelberg
Computer Science; Database Management
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