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.