Checking well-definedness of XQueries

Опубликовано 6 сентября 2016, 5:04

XQuery is the upcoming standard language for querying XML data. The dynamic semantics of XQuery is defined in such a way that the evaluation of an XQuery expression may crash (raise a run-time error). When an XQuery never crashes we say that it is well-defined. Automatic checking for well-definedness is, of course, undecidable. Nevertheless, for certain interesting fragments of XQuery that are similar in expressiveness to standard relational query languages, well-definedness can become decidable. Important choices in this respect are whether we use a set- or a list-semantics for XML data, and whether we follow the XQuery convention to identify a single element with the list consisting of only that element.