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Re: XPath and XPattern (was Re: More on tamingSAX)

• To: kjouk@y...
• Subject: Re: XPath and XPattern (was Re: More on tamingSAX)
• From: Uche Ogbuji <uche.ogbuji@f...>
• Date: Fri, 24 Dec 2004 07:36:51 -0700
• Cc: xml-dev@l...
• In-reply-to: <200412241130.59409.kjouk@y...>
• Organization: Fourthought, Inc.
• References: <E1ChXnb-0004PJ-00@u...> <41CB29FA.8010201@t...> <200412241130.59409.kjouk@y...>
• User-agent: Mozilla Thunderbird 0.9 (X11/20041127)

Kevin Jones wrote:

>On Thursday 23 December 2004 20:26, Oleg Tkachenko wrote:
>  
>
>>It would be really nice to have such streamable XPath
>>subset strictly defined (and probably with different
>>name). 
>>    
>>
>
>My understanding is that full XPath is streamable in the 
>context of whole document scans, i.e. there is strictly 
>speaking no need to subset. The problem case is for partial 
>scans, i.e. XPath execution from a context node. This makes 
>the solution less appealing as it has less practical use, 
>say in XSLT. Of course subsetting XPath to make it easier 
>to implement in a streaming model may be a good goal 
>itself.
>  
>

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.

In other words, everyone understands well the distinctions you're trying 
to point out, but we're more interested in a descriptive name than in 
quiddities.

BTW, I don't know what you mean by "XPath execution from a context 
node".  XPath *always* has a context node.  Someone told me once that 
some working group was trying to define a host language for XPath that 
did not define a context node.  I told them this is a case of people 
*thinking* they're using XPath, but rather using some creature of their 
own invention.


-- 
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

• Follow-Ups:
  • Re: XPath and XPattern (was Re: More on taming SAX)
    • From: Kevin Jones <kjouk@y...>

• References:
  • RE: XPath and XPattern (was Re: More on taming SAX)
    • From: "Michael Kay" <mike@s...>
  • Re: XPath and XPattern (was Re: More on tamingSAX)
    • From: Oleg Tkachenko <oleg@t...>
  • Re: XPath and XPattern (was Re: More on taming SAX)
    • From: Kevin Jones <kjouk@y...>

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