Deciding well-definedness of XQuery fragments

Abstract

Unlike in traditional query languages, expressions in XQuery can have an undefined meaning (i.e., these expressions produce a run-time error). It is hence natural to ask whether we can solve the well-definedness problem for XQuery: given an expression and an input type, check whether the semantics of the expression is defined for all inputs adhering to the input type. In this paper we investigate the welldefinedness problem for non-recursive fragments of XQuery under a bounded-depth type system. We identify properties of base operations which can make the problem undecidable and give conditions which are sufficient to ensure decidability.