Re: xpath processing brain dead

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: James Pye <lists(at)jwp(dot)name>
Cc: Peter Eisentraut <peter_e(at)gmx(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Nikolay Samokhvalov <samokhvalov(at)gmail(dot)com>
Subject: Re: xpath processing brain dead
Date: 2009-02-27 02:03:47
Message-ID: 49A74A03.6060508@dunslane.net
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James Pye wrote:
> On Feb 26, 2009, at 5:41 PM, Andrew Dunstan wrote:
>>> http://www.exslt.org/exsl/functions/node-set/index.html
>>
>> A node-set isn't a document.
>
> yes.. :)
>
> I guess what I'm saying is that if:
>
> tinman=# SELECT XML'<foo/><bar/>';
> xml
> --------------
> <foo/><bar/>
> (1 row)
>
> is considered to be valid per *SQL-XML*, then it should probably be
> treated as a node-set in the context of xpath, not mangled with
> <x>...</x>..
>
> Certainly, I would expect an implicit "node-set() call" long before
> wrapping the fragment in <x>...</x> and prefixing my xpath query.
>
> However, I find the validity of the above, XML'<foo/><bar/>', a bit
> disturbing to begin with. :P
>
>> In any case, this functionality doesn't appear to be in libxml2,
>> it's in libxslt according to the reference you provided.
>
> I think that's *just* referencing the list of xslt implementations
> that the extension function is known to be available in.. I doubt that
> means to imply that the function or equivalent functionality is not
> available in libxml2 itself. I'd wager that equivalent functionality
> could be implemented if it weren't directly/already available.. =)
>

James,

can you point me at any call in libxml2 which will evaluate an xpath
expression in the context of a nodeset instead of a document? Quite
apart from anything else, xpath requires there to be a (single) context
node (see http://www.w3.org/TR/xpath20/#context ). For a doc, we set
that node to the document node, but what would it be for a node-set or a
fragment? If we can't get over that hurdle we're screwed in pursuing
your line of thought.

cheers

andrew

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