We study structural properties of each of the main sublanguages of XPath  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.
|Title of host publication||Database Theory - ICDT 2003|
|Subtitle of host publication||9th International Conference, Siena, Italy, January 8-10, 2003, Proceedings|
|Publisher||Springer Berlin Heidelberg|
|Number of pages||17|
|Publication status||Published - 2003|