XQL and XPointer

Paul Prescod paul at prescod.net
Wed Mar 31 20:35:20 BST 1999

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"," ",...,
 Paul Prescod  - ISOGEN Consulting Engineer speaking for only himself

"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

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