Section: New Results

XQuery and Static Typing

XQuery is a functional language dedicated to XML data querying and manipulation. As opposed to other W3C-standardized languages for XML (e.g. XSLT), it has been intended to feature strong static typing. Currently, however, some expressions of the language cannot be statically typed with any precision.

In [20] , we argue that this is due to a discrepancy between the semantics of the language and its type algebra. We discuss how to handle this discrepancy by improving the type system. We describe a logic-based language of extended types able to represent inner tree nodes and show how it can dramatically increase the precision of typing for navigation expressions. We describe how inclusion between these extended types and the classical regular tree types can be decided, allowing a hybrid system combining both type languages. The result is a net increase in precision of typing.

In a previous work, we aimed at bridging the gap between path-based XML processing languages like XQuery and pattern-based such languages like CDuce. We extend the language CDuce into a succinct core $\lambda$-calculus that captures XQuery 3.0. The extensions we consider essentially allow CDuce to implement XPath-like navigational expressions by pattern matching and precisely type them. The elaboration of XQuery 3.0 into the extended CDuce provides a formal semantics and a sound static type system for XQuery 3.0 programs.