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Re: XPath and XPattern (was Re: More on taming SAX)

• To: Uche Ogbuji <uche.ogbuji@f...>
• Subject: Re: XPath and XPattern (was Re: More on taming SAX)
• From: Kevin Jones <kjouk@y...>
• Date: Fri, 24 Dec 2004 16:18:32 +0000
• Cc: xml-dev@l...
• In-reply-to: <41CC2983.3020009@f...>
• References: <E1ChXnb-0004PJ-00@u...> <200412241130.59409.kjouk@y...> <41CC2983.3020009@f...>
• Reply-to: kjouk@y...
• User-agent: KMail/1.6.2

On Friday 24 December 2004 14:36, Uche Ogbuji wrote:
> Kevin Jones wrote:
>
> Of course XPath is always streamable, if you have no
> practical limitations (e.g. you're willing to store all
> node data and implement unbounded look-ahead).  When
> people speak of a "streamable subset", they mean a subset
> that works practically with most streaming host
> languages, meaning that these host languages should not
> have to compromise too much memory or state complexity in
> order to satisfy the scope of node requests from the
> XPath subset.

Hi,

I was probably being a little brief. I was not intending 
just to comment that XPath was theoretically possible, but 
the assumption you need a subset for this case may be 
wrong. Taking the examples of storing all node data and 
unbounded look-ahead, clearly neither of these are 
requirements of streaming XPath, just features of some way 
of implementing it.

I would say that having written/supported one streamable 
subset for a few years they never implemement enough. Some 
of the harder features to implement in a streamable way are 
just the ones that make XPath better than any old pattern 
language, e.g. predicates as expressions.

>
>
> BTW, I don't know what you mean by "XPath execution from
> a context node".  XPath *always* has a context node. 

Loose language, I meant as apposed to the context node being 
the document root which is a special case that allows 
reverse axis removal via path re-writing. 

Kev.

• Follow-Ups:
  • Re: XPath and XPattern (was Re: More on tamingSAX)
    • From: Uche Ogbuji <uche.ogbuji@f...>

• References:
  • RE: XPath and XPattern (was Re: More on taming SAX)
    • From: "Michael Kay" <mike@s...>
  • Re: XPath and XPattern (was Re: More on taming SAX)
    • From: Kevin Jones <kjouk@y...>
  • Re: XPath and XPattern (was Re: More on tamingSAX)
    • From: Uche Ogbuji <uche.ogbuji@f...>

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