Checking well-definedness of XQueries

October 20, 2004
Jan Van den Bussche | Limburgs Universitair Centrum, Belgium

XQuery is the upcoming standard language for querying XML data. The dynamic semantics of XQuery is defined in such a way that the evaluation of an XQuery expression may “crash” (raise a run-time error). When an XQuery never crashes we say that it is well-defined. Automatic checking for well-definedness is, of course, undecidable. Nevertheless, for certain interesting fragments of XQuery that are similar in expressiveness to standard relational query languages, well-definedness can become decidable. Important choices in this respect are whether we use a set- or a list-semantics for XML data, and whether we follow the XQuery convention to identify a single element with the list consisting of only that element.

Speaker Details

Jan Van den Bussche is professor of theoretical computer science at the Limburgs Universitair Centrum, Belgium. He received his PhD from the University of Antwerp, Belgium, in 1993, under Jan Paredaens. He has primarily worked on the foundations of database systems. Other research interests are ASMs (Gurevich’s abstract state machines), the Web, data mining, and bioinformatics. He chairs the council of the International Conference on Database Theory, and will chair the program committee of the 2006 ACM Symposium on Principles of Database Systems.