- From: <scott_boag@us.ibm.com>
- Date: Wed, 9 Mar 2005 11:08:36 -0500
- To: Frank Yung-Fong Tang <franktang@gmail.com>
- Cc: public-qt-comments@w3.org
Actually, a colleague of mine (who can identify himself if he wants), as corrected me: ======== ...although the grammar used for parsing is a context free grammar, XQuery's very likely a context sensitive language, as are most programming languages, due to the additional constraints placed on the language by the prose in the XQuery document - for instance, variables must be declared before they're used, they can't be twice declared, etc. Those constraints can typically be described only by using a context sensitive grammar, but not a context free grammar. It's not worth the bother to define context sensitive grammars that enforce those constraints, so everybody uses context free grammars and parsers for them with additional constraint checking built on top. ========= (I was thinking of the language more in terms of the syntax. In any case, it's all a bit academic.) -scott Scott Boag/Cambridge/IBM wrote on 03/09/2005 06:28:11 AM: > > Is the language expressed by XQuery (not the XQuery grammar itself, > > but the expression power carried by XQuery) > > You've lost me here. The language is described by the grammar. > > > a Conext Free Grammar or > > Context Sensitive Grammar? > > XQuery has a Context free grammar, and is a context free language. > But every context-free language is context-sensitive (but not every > context-sensitive language is context-free), so there you go. See > http://en.wikipedia.org/wiki/Chomsky_hierarchy. > > -scott
Received on Wednesday, 9 March 2005 16:44:08 UTC