XQL and XPointer

[Paul Prescod]

Oren Ben-Kiki asks:
> Actually, what is the difference between XPointer syntax and XQL (as defined
> above)? Both allow matching elements according to the structure of the XML
> tree and/or the value of attributes. The syntax is different and the set of
> capabilities doesn't exactly match. Is it just due to historical reasons
> that XSL isn't using (possibly enhanced) XPointers in its match patterns?

Yes the reasons are mostly historical but there are technical issues. The
XPointer "model" is to select a contiguous, perhaps non-well formed range
of data. The XSL model is to select a list of well-formed, perhaps
non-contiguous nodes.

I don't think that there is anything wrong from a hypertext-theoretic
point of view with having pointers return non-contiguous nodes. And you
can simulate non-well-formedness:

This is text <EMPH>and this is some</EMPH> more text.
     ^                      ^

In this case we could simulate a link from the first occurence of "is" to
the second by selecting the nodes "i","s"," ","t","e","x","t"," ",...,
etc.
-- 
 Paul Prescod  - ISOGEN Consulting Engineer speaking for only himself
 http://itrc.uwaterloo.ca/~papresco

"Perpetually obsolescing and thus losing all data and programs every 10
years (the current pattern) is no way to run an information economy or
a civilization." - Stewart Brand, founder of the Whole Earth Catalog
http://www.wired.com/news/news/culture/story/10124.html

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