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Re: What class of grammars is an XPath?

• From: Michael Kay <mike@saxonica.com>
• To: xml-dev@lists.xml.org
• Date: Thu, 27 Jan 2011 14:19:41 +0000

On 27/01/2011 13:26, Dimitre Novatchev wrote:
>> Anyway, it is an interesting question. I think the same question could be
>> asked, rephrased, as "what is the smallest class of formal grammars that
>> every Xpath (evaluating to boolean) belongs to?"
> It isn't a regular expression -- XPath expressions may have an
> unlimited nestedness.
>
> It is definitely a context-free (CF) grammar and even more
> specifically, it is an LR(1) grammar.
>
> Three years ago I defined the full XPath 2.0 grammar (with one
> exception

Ah, you have interpreted the question quite differently from me (and 
perhaps correctly?) I thought it was looking at XPath as a grammar in 
which the sentences being described are document instances. You are 
talking about the grammar in which XPath expressions are the sentences.

Michael Kay
Saxonica

• Follow-Ups:
  • Re: What class of grammars is an =?UTF-8?Q?XPath=3F?=
    • From: rjelliffe <rjelliffe@allette.com.au>
  • Re: What class of grammars is an XPath?
    • From: Dimitre Novatchev <dnovatchev@gmail.com>

• References:
  • Which algorithm do XML Schema validators use to decide if a stringmatches a regular expression?
    • From: "Costello, Roger L." <costello@mitre.org>
  • Re: Which algorithm do XML Schema validators use to decideif a string matches a regular expression?
    • From: Michael Kay <mike@saxonica.com>
  • What class of grammars is an =?UTF-8?Q?XPath=3F?=
    • From: rjelliffe <rjelliffe@allette.com.au>
  • Re: What class of grammars is an XPath?
    • From: Dimitre Novatchev <dnovatchev@gmail.com>