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Labeled diagram and figure questions

From: <osserman@math.mit.edu>
Date: Sat, 28 Jun 2003 00:54:39 -0400
Message-Id: <200306280454.h5S4sdM11123@lagrange.mit.edu>
To: www-math@w3.org

   I have been looking at the MathML spec, and I had some questions 
regarding intentions for labeled diagrams and figures, both of which
arise frequently in my field (algebraic geometry). I apologize if these
issues have come up before, or if I missed something in the spec, but I
couldn't find answers to these questions either in the spec or the list
   As far as I have been able to tell, the current intent for, say,
commutative diagrams, is to offer limited support via mtable. However,
I am not clear on exactly what the capabilities in this regard would be.
It seems that one could do unlabeled diagrams, even with diagonal arrows,
but that labeling the arrows (other than horizontal ones) might not be
possible. Is this correct? What is the rationale for not having some degree
of explicit labeled diagram, perhaps along the lines of what the xymatrix
package offers in latex? 
   Along the same lines, I was looking through the list of arrows available,
and I was able to find most of the simplest ones that would be likely to
come up in diagrams, but I couldn't find two fairly common ones: dotted and
two-headed (ie, for surjective maps) diagonal arrows. These seem to me to be
far more basic than a number of the arrow symbols which are included; am I
just missing them somewhere?
   Finally, with regard to images, I see that you have decided to omit any
specific support for them. While I can appreciate your attitude that content
such as labeled diagrams would work better on a philosophical level as a 
structured graphics/label encoded entity than an image, and I wholeheartedly
agree that such a construction is desireable, given that you have decided to
not include such a construction, I'm not sure I see the wisdom in choosing
to not support the obvious fallback construction, which is to say diagrams
as images. If there is no general labeled diagram facility, and no support
for images for "complicated commutative diagrams", what do you recommend
that authors do when they have such a diagram?
   I also take issue with the assertion that glyphs and labeled diagrams are
the primary situations where one would want to use an image (at least,
presuming that 'glyphs' is in reference to representations of characters and
atomic symbols; I'm not sure what the standard usage is). The most
obvious alternative is figures, which are widely used throughout geometry,
topology, and calculus, and which I believe semantically make more sense
than labeled diagrams to be encoded as images. It seems to me that simple
support for images with MathML tags placed at specified locations (similar
to xfig's support for figures encoded in a combined ps/latex format) would
give the semantically and practically desireable implementation for figures,
and would also provide a very workable backup plan for labelled diagram
implementation until something more robust can be adopted in the future. 
   I would be very interested to hear what the working group's perspective
is on these issues. 
   Thank you for your assistance,

Received on Saturday, 28 June 2003 01:13:47 UTC

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