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   RE: XLink transformations

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  • From: Steve Boyce <SteveB@hbs.com>
  • To: "'Bullard, Claude L (Len)'" <clbullar@ingr.com>,"'xml-dev@xml.org'" <xml-dev@xml.org>, 'Kay Michael' <Michael.Kay@icl.com>
  • Date: Tue, 18 Jul 2000 15:41:21 +0100


Thanks for the replies (and especially Claude's notes 1-7), which I very
much appreciated.  Thoughts such as Claude's were indeed behind my question
as I did maths at uni 20 years ago... and still have vague memories...

Anyway, the point where I started is that documents get transformed through
a whole XSLT pipeline and it just looks to me like XPath struggles with this
(or rather, doesn't cope at-all).  But this is probably getting off-topic
and my thoughts are probably as ill-formed as most of the XML I produce, so
here are just a few further comments:

> Some stylesheets can be written to process XML usefully regardless of its
Sure, e.g. the identity transform.  There would have to be a universal
schema U of all well-defined XML docs. 

> XLink isn't an instance of XSLT
Sure I understand that XPath as it's defined is not a transformation, my
point was that what it was trying to achieve could perhaps be alternatively
thought of in that way. i.e. If I have a schema then there is a set of
schemas <b>S</b>, all the schemas enabling links between the elements of S.
(Looking at Claude's note 5 this is probably an equivalence relation of some
kind as all you are doing is adding some (conceptual) <A>s basically).  What
would such schemas look like and what would possible mappings from S to them
look like?  

> Unlike SGML <snip>
Sure, I know nothing of SGML and understand that these issues may have been
addressed there and got lost from XML.

> [vaguely addressing some of Claude's other points, esp. 6]
I think one could define "restrictions" of schemas i.e. a restricted schema
S(R) of S would be one where every transform S(R) -> S had an inverse. (i.e.
you lose information going from S(R) to S).  I think schemas generated by
XPath would be restrictions for instance.  Words like "equivalence relation"
are drifting through my head.

Anyway, to sum up, it still seems to me that a given XSLT transform can only
be meaningful within the context of its source and destination schemas, and
XLink "defines a transformation" (implicitly) from a document in a schema S
to a document in a schema S', and (although S' is quite closely bound to S
as Claude points out) it still seems like a transformation which maps from
schema S to schema T is going to hit problems if one tries to apply it to
get from  S' to T.  Unless someone can work out some general rules.
Unfortunately I don't have anything concrete to offer on that front. 

Thanks again, the replies were very much appreciated, I'll go back into
hiding now.  



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