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   Re: [xml-dev] XPath and XPattern (was Re: [xml-dev] More on tamingSAX)

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Kevin Jones wrote:

>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.
>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 think I've used some loose language of my own.  I tried to be a bit 
more scrupulous in my last post:


Does the conceptualization I present at the end of that posting help 
clarify the idea of an "XPath subset friendly to SAX processors"?

>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.

This is true, somewhat unfortunately.

Uche Ogbuji                                    Fourthought, Inc.
http://uche.ogbuji.net    http://4Suite.org    http://fourthought.com
Use CSS to display XML - http://www.ibm.com/developerworks/edu/x-dw-x-xmlcss-i.html
Full XML Indexes with Gnosis - http://www.xml.com/pub/a/2004/12/08/py-xml.html
Be humble, not imperial (in design) - http://www.adtmag.com/article.asp?id=10286
UBL 1.0 - http://www-106.ibm.com/developerworks/xml/library/x-think28.html
Use Universal Feed Parser to tame RSS - http://www.ibm.com/developerworks/xml/library/x-tipufp.html
Default and error handling in XSLT lookup tables - http://www.ibm.com/developerworks/xml/library/x-tiplook.html
A survey of XML standards - http://www-106.ibm.com/developerworks/xml/library/x-stand4/
The State of Python-XML in 2004 - http://www.xml.com/pub/a/2004/10/13/py-xml.html


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