Structural Properties of XPath Fragments Michael Benedikt, Wenfei Fan, and Gabriel M. Kuper   View Paper (PDF)   Return to Research Papers Abstract commonly used in practice. First, we characterize the expressive power of these language fragments in terms of both logics and tree patterns. Second, we investigate closure properties, focusing on the ability to perform basic Boolean operations while remaining within the fragment. We give a complete picture of the closure properties of these fragments, treating XPath expressions both as functions of arbitrary nodes in a document tree, and as functions that are applied only at the root of the tree. Finally, we provide sound and complete axiom systems and normal forms for several of these fragments. These results are useful for simplification of XPath expressions and optimization of XML queries. BIBTEX  Lecture Notes in Computer Science  Publisher: Springer-Verlag Heidelberg  ISSN: 0302-9743  Subject:  Computer Science  Volume 2572 / 2003  Title:  : Database Theory - ICDT 2003: 9th International Conference Siena, Italy, January 8-10, 2003. Proceedings  Editors:  D. Calvanese, M. Lenzerini, R. Motwani (Eds.) :  Chapter: pp. 79 - 95 }, ©2005 Association for Computing Machinery