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FW: MathML-Presentation specs criticized.

From: Jimmy Cerra <jimbofc@yahoo.com>
Date: Tue, 16 Apr 2002 18:36:08 -0400
To: <www-math@w3.org>
Message-ID: <000101c1e597$1d92b1e0$0100a8c0@locutus>
Sorry: forgot to post it... More people may want to help me with my questions.

>> the layout is part of the content, so the presentation language should
>> allow multiple layouts of the same code.
> No, that is what the content markup is for. <and-more/>

I disagree.  The layout of mathematical expression often lends some additional
meaning.

For instance, a derivative can be displayed visually as a prime to accentuate
the fact that it is a separate transformation of the original function.  A
similar way of writing the derivative is with an upper-script of a dot -
allowing a distinction between geometric transformations (also historically
marked up with a prime) and the derivative.  In a completely different notation,
it is often displayed as a fraction to help emphasize the chain rule.  A fourth
way a derivative can be displayed is the function with a subscript of the
variable of differentiation - a way often used to highlight (getting out my
thesaurus :) that variable.  Thus one function (the derivative, in the above
case) can have different representations (note that these layouts are not
necessarily media-dependent).

If content markup is used to explicitly define the function (derivative), then
some other content (of which property of the derivative to accentuate) is lost.
However, presentation markup is often not explicit enough (EX: is this a
fraction or a real derivative?).  Thus the separation of presentation and
content markup schemes cannot contain the full meaning of the mathematical
expression.

Although presentation and content markup can be combined, <em>they cannot be
combined on the same expression</em>.  Thus the author of a MathML document has
to make a choice between ambiguous presentation markup and meaning-neutered (as
opposed to accentuated meaning) content markup.

You said that Presentation and Content are separated in MathML?  How?  One or
the other can be used, or both at the same time.  However, there is no way to
change the presentation at whim (ie, loading another style-sheet).  To change
the presentation the markup tags must be edited - much as the font tags and
style-attributes of HTML3.2 had to be changed to change the style of the
document (hence the reason for CSS).  Is there another way; can you give an
example?




> That's one reason for having specific mathematical layout rather than just
> re-using generic css styling...
> <snip/>
> ...it is still essentially the layout that is being specified, not the
> mathematical concept of division.

As I argued above, there should be a way of combining both the (media
independent) layout and the mathematical concept of division.  If I currently
understand the specs correctly, layout and math-concept markup can be combined,
but only under specific rules.

More importantly, I don't see how a specific layout markup can be specified to
be a specific content as well.  This is important as the layout is part of the
content of the expression (as I argued before).

Or I might be wrong.  Is there way?
---
Jimmy Cerra

P.S.  I wish there was a decent book or online tutorial (not the specs or an
introductory tutorial), which dealt with many questions that users (well, just
I) have.




-----Original Message-----
From: www-math-request@w3.org [mailto:www-math-request@w3.org] On Behalf Of
David Carlisle
Sent: Tuesday, April 16, 2002 3:38 AM
To: jimbofc@yahoo.com
Cc: www-math@w3.org
Subject: Re: MathML-Presentation specs criticized.


> the layout is part of the content, so the
> presentation language should allow multiple layouts of the same code.

No, that is what the content markup is for. Content markup has a default
presenatation form but my be presented in any visual or non visual
format chosen by the rendering agent. But you need some method of
specifying mathematical layouts, that's what the presentation elements
are for. If you want to unambiguously express the idea of a fraction use
<apply><divide/>
<mfrac>expresses the notion of a mathematical layout scheme involving
two terms laid out vertically with a line between. If you know the
context you can of course infer meaning from this mathematical layout
but it is always context dependent.


> (Here's a good (I hope) example.  Visual rendering agents might style an
> mfrac element as two rows separated by a bar.  However, a blind person's
> audio rendering agent might style the mfrac element by saying the
> (insert natural language here) translation of the numerator + "over" +
> the denominator.  The blind person would be confused if it was rendered
> as the numerator + "1 pixel solid bar" + denominator.)

That's one reason for having specific mathematical layout rather than just
re-using generic css styling, mfac can be rendered as "over" in an aural
rendering wheras general css lines are probably ignored altogether as
css styling is purely decorative. But whether it's rendered as two terms
with a line or two spoken phrases and teh word over, it is still
essentially the layout that is being specified, not the mathematical
concept of division.

David
Received on Tuesday, 16 April 2002 18:36:01 GMT

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