Guest editorial

Guest editorial The VLDB Journal (2000) 9: 1 The VLDB Journal c Springer-Verlag 2000 This special issue brings together a set of papers that ad- Mary Fernandez, Daniela Florescu, Alon Levy and Dan dress some of the areas of intersection between database Suciu in the paper “Declarative specifcation of web sites technology and the World Wide Web. This intersection is with fast becoming a key focus of database research, with mul- Strudel”, provide a comprehensive description of Strudel, tiple facets that touch many different aspects of database a system for implementing “data-intensive” web sites. Ma- systems. As semistructured data and XML become preva- jor features of the system are the distinction of three levels lent, data models and query languages for them must be (data, structure, and presentation) and the use of a declarative proposed, studied, and implemented. As database systems query language for the specification of the structure of sites. become key components in the construction of large web The paper also contains an a posteriori discussion of some sites, new sets of requirements must be incorporated. Query experiences and brief indications about three “successors” optimization in the Web environment poses new challenges of Strudel. and requires new techniques. In the paper “Analysing navigation behaviour in web The five papers in this issue were selected from among sites integrating multiple information systems”, Bettina the fourteen that were submitted in response to our call for Berendt and Myra Spiliopoulou discuss how the navigation papers. Each paper was reviewed, and for each them two behavior of web users can be analyzed to evaluate the qual- rounds of reviews were made possible by the enthusiastic ity of a site (with specific reference to sites that dynamically cooperation provided by our reviewers. generate pages in response to queries specified by filling The first paper in this issue, “Semantic caching of web forms). The analysis is based on the WUM environment, queries”, by Boris Chidlovskii and Uwe M. Borghoff tackles proposed by one of the authors in a previous paper, and is performance problems of “web queries” (intended as queries demonstrated with an experiment on a large real site. asked for by means of meta-searchers, which return the tu- In the final paper of the issue “UnQL: a query language ples that satisfy a given Boolean condition). More precisely, and algebra for semistructured data based on structural re- the paper considers conjunctive queries and studies how “se- cursion”, Peter Buneman, Mary Fernandez and Dan Suciu mantic caching” can be useful. The cache maintains regions, present the full details of a language for semistructured data and when a query is issued, part of the result is found in the and XML. The paper is theoretical in nature, but the lan- cache and only the “remainder” is retrieved over the net. guage has a strong motivation regarding the current interest The paper “Learning response time for WebSources us- in semistructured data and XML. Various formal results are ing query feedback and application in query optimization” by shown, some of which could find application in the imple- Jean-Robert Gruser, Louiqa Raschid, Vladimir Zadorozhny mentation of query languages for XML. and Tao Zhan also considers performance issues, but from We thank all the authors who submitted papers to this a different point of view. The goal is to predict, by means special issue, as well as the anonymous referees for their of learning techniques, the response time of a Web source. disinterested and essential contribution. It also shows how the predictions can be used by a scram- bling optimizer, that is, an optimizer that changes a query execution plan. Paolo Atzeni and Alberto O. Mendelzon The VLDB Journal Springer Journals
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Copyright © 2000 by Springer-Verlag Berlin Heidelberg
Computer Science; Database Management
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