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

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On Thu, 2004-12-23 at 22:12 +0000, Michael Kay wrote:
> > There's also the question of context -- would the only context be the
> > stack, or do people hope to have access to left siblings as well?
> I found it very useful also to have a one-event lookahead.

I agree this is useful, but is it awkward to start putting such specisl
rules on certain axes?  I think a straightforward streamable subset is
an all-or-nothing prospect with regard to XPath axes:

ancestor: all accessible
parent: all accessible
self: all accessible

all other axes: none accessible (ignore the crazy axes preceding and
following as a simplifying assumption :-) )

One event lookahead would mean a more nuanced rule along the lines of

child: accessible only for position() = 1

My guess is that this makes things a little less neat, but maybe that's
a fair trade-off for the usefulness.

Maybe the way to go is to allow

descendant: all accessible
child: all accessible

This should still be streamable in any implementation scenario I can
think of: it just complicates the state table a great deal.

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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