On the expressibility of functions in XQuery fragments

XQuery is a powerful XML query language with many features and syntactic constructs. For many common queries we do not need all the expressive power of XQuery. We investigate the effect of omitting certain features of XQuery on the expressive power of the language. We start from a simple base fragment which can be extended by several optional features being aggregation functions such as count and sum, sequence generation, node construction, position information in for loops, and recursion. In this way we obtain 64 different XQuery fragments which can be divided into 17 different equivalence classes such that two fragments can express the same functions if they are in the same equivalence class. Moreover, we investigate the relationships between these equivalence classes and derive some properties of the fragments within these equivalence classes.

[1]  Jan Hidders,et al.  A Light but Formal Introduction to XQuery , 2004, XSym.

[2]  Leonid Libkin,et al.  Expressive power of SQL , 2001, Theor. Comput. Sci..

[3]  Gabriel M. Kuper,et al.  Structural properties of XPath fragments , 2003, Theor. Comput. Sci..

[4]  Maarten Marx,et al.  Conditional XPath, the first order complete XPath dialect , 2004, PODS.

[5]  Anahí Gallardo Velázquez,et al.  Conference , 1969, Journal of Neuroscience Methods.

[6]  Li Chen.  Proceedings of the Twenty-fourth ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, June 13-15, 2005, Baltimore, Maryland, USA , 2005, PODS.

[7]  Dan Suciu,et al.  Database and XML Technologies: Second International XML Database Symposium, XSym 2004, Toronto, Canada, August 29-30, 2004, Proceedings , 2004 .

[8]  Georg Gottlob,et al.  The complexity of XPath query evaluation , 2003, PODS.

[9]  Stijn Vansummeren,et al.  Deciding well-definedness of XQuery fragments , 2005, PODS '05.

[10]  Jan Hidders,et al.  On the Expressive Power of Node Construction in XQuery , 2005, WebDB.

[11]  Christoph Koch,et al.  On the complexity of nonrecursive XQuery and functional query languages on complex values , 2006, TODS.

[12]  Peter Buneman,et al.  Semistructured data , 1997, PODS.

[13]  Michele Bugliesi,et al.  Automata, Languages and Programming: 33rd International Colloquium, ICALP 2006, Venice, Italy, July 10-14, 2006, Proceedings, Part II (Lecture Notes in Computer Science) , 2006 .

[14]  Jan Paredaens,et al.  On the Expressive Power of the Relational Algebra , 1978, Inf. Process. Lett..

[15]  Scott Boag,et al.  XQuery 1.0 : An XML Query Language , 2007 .

[16]  Stephan Kepser,et al.  A Simple Proof for the Turing-Completeness of XSLT and XQuery , 2004, Extreme Markup Languages®.

[17]  Michael Benedikt,et al.  Interpreting Tree-to-Tree Queries , 2006, ICALP.