Section: New Results

XQuery Static Type-Checking

In the context of our ongoing work on XQuery static type-checking [3], we extended our type system and improved the associated software accordingly (see Sec. 5.5 and 5.4). The type language it is based on is now a subset of RelaxNG+Schematron (instead of DTDs), which is novel in the context of static typing: Schematron is normally used to validate a document after it has been generated, whereas our system is able to ensure statically that a program will always generate a valid document.

Schematron constraints present the advantage of describing some properties in a very concise way compared to schema languages based on regular tree types, e.g. it allows writing in one line that nested anchors are forbidden in HTML, a constraint which appears in the specification but not in the formal DTD schema because of the verbosity it would involve.