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Re: What class of grammars is an XPath?

• From: Dimitre Novatchev <dnovatchev@gmail.com>
• To: Michael Kay <mike@saxonica.com>
• Date: Thu, 27 Jan 2011 08:23:43 -0800

> 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.

Exactly.


Actually, Rick is asking also about a sublanguage:

>>> 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?"

The rules for boolean expression include the rules for any XPath
expression, so the answer remains exactly the same.


-- 
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
Facts do not cease to exist because they are ignored.



On Thu, Jan 27, 2011 at 6:19 AM, Michael Kay <mike@saxonica.com> wrote:
> 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
>
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• 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>
  • Re: What class of grammars is an XPath?
    • From: Michael Kay <mike@saxonica.com>