A Fixed-Point Query Language for XML
Qing Wang, Klaus‐Dieter Schewe, Bernhard Thalheim · European Journal of Combinatorics · 2009
In order to increase the expressiveness of XML query languages we define an XML object model that provides a rich description of XML data using the notions of class schema and class tuple. Based on this model we develop a novel query language, the XML Identity Query Language (XIQL) based on identifier generation and fixed-point computation. However, XIQL cannot deal with finite tree duplicates in an XML object graph. To solve this problem we extend XIQL by integrating terms $\breve{t}$ denoting hereditarily finite sets. With respect to determinate transformations the extended XIQL+ is still incomplete, but becomes complete with respect to a modified completeness criterion for XML database transformations, which aims at capturing more non-determinism.