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RE: XSLT question on transitive closures

  • From: "Michael Kay" <mike@s...>
  • To: "'Rick Jelliffe'" <rjelliffe@a...>,<xml-dev@l...>
  • Date: Fri, 26 Oct 2007 10:09:44 +0100

RE:  XSLT question on transitive closures
> Am I right in thinking that 
> 1) XPath2 functions don't have have a function for transitive 
> closure (along provided xpaths)

Transitive closure is intrinsically a higher-order function, and XPath 2.0
sadly doesn't have higher-order functions. I'm pushing to get them into some
future version, but there's not a high level of enthusiasm in the working
> 2) SAXON 8 does not have the saxon:closure() extension 
> function that older versions of SAXON had

Looking at the change log, it was withdrawn "temporarily" in Saxon 7.0
because of problems with its use of the current() function. If I remember
rightly, there were some implementation problems caused with the function's
use of the evaluation context and these revealed some fairly deep
inadequacies in the spec. I never did get to put it back, which I can
attribute to no-one complaining that it had been taken out. (I've tended,
quite wrongly, to imagine my users moving forward one release at a time and
providing feedback along the way. Unfortunately this means that the users
who stayed put with 6.5.x for years and are now making the move to 8.9 in a
single step have had little influence on the direction the product has taken
in the meantime.)
> 3) The one to use is probably still Christian Nentwich's code 
> from circa 2001 as adopted into EXSLT ?
I think it would be nice to do it properly based on FXSL higher-order
functions, which are much more cleanly specified. Perhaps there is already a
suitable function in FXSL. 

The other thing that's needed is the ability to check for cycles. Simply
blowing the stack or looping isn't good enough.

Incidentally, such questions might be better addressed over on xsl-list.

Michael Kay

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