W. Eliot Kimber eliot at
Mon Mar 23 17:57:07 GMT 1998

At 10:02 AM 3/23/98 -0000, Michael Kay wrote:

>I would be more enthusiastic about the XLL approach if it
>wasn't so full of hyperlink behaviour. I want to model a 
>relationship between two objects that happen to be in different
>datasets. All the XLL stuff about the manner in which links are
>followed is to me entirely presentation-oriented and I don't
>want it in my data thankyou very much. From that point of
>view I prefer the IDREF style of specification which says
>nothing about the behavioural characteristics of the link.
>What I really need is a "distributed IDREF".

It sounds like what you want is what HyTime provides: more general and
robust link representation and addressing methods that don't imply any
specific behaviors (which HyTime considers to be presentation/behavior
style beyond its ken).

Note that Xpointers can be used witin a HyTime context because HyTime
allows you to use any addressing method you want with hyperlinks (or any
other use of addressing). Xpointers can be formally defined in terms of
operations on groves, which is all you need to do to make it make sense in
a HyTime processing context (not counting implementation of support for the
query  notation in your system).

Note also that both the simple and extended link elements can be formally
defined as specializations of the HyTime hylink (simple) and varlink
(extended) forms, which means that you can view XLink as a specialized
application of HyTime, one that adds specific behavior and description
semantics to HyTime's basic structures.

Here's a tip: if you've implemented support for simple and extended,
implementing support for the rest of HyTime's hyperlink forms is an almost
trivial exercise (doing full HyTime semantic validation would require a bit
more effort). If you've implemented Xpointers, implementing HyTime's
built-in addressing elements is mostly an application of the code that
implements the Xpointer fundamentals (it's a bit more complicated because
you have to deal with indirection and such, but it's not rocket science).

For more information about HyTime, see the following Web sites:

-, the HyTime user's group Web site.
-, TechnoTeachers' web site, where you'll find lots of 
  good information, as well as the HyBrowse demonstration HyTime browser
  (it's out of date in that it doesn't support HyTime 2nd Edition, but it's
  still a useful demonstration and learning tool)
-, the ISOGEN demo area, where you'll find some
  sample HyTime implementations of various sorts
-, the ISO/IEC JTC1/WG4 web site, where you can find
  information about HyTime and its related standards.


<Address HyTime=bibloc>
W. Eliot Kimber, Senior Consulting SGML Engineer
Highland Consulting, a division of ISOGEN International Corp.
2200 N. Lamar St., Suite 230, Dallas, TX 95202.  214.953.0004

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