xml-dev - Re: Separation of formatting...

["Rick Jelliffe" <ricko@allette.com.au>]

From: Gregg Reynolds <greyno@mcs.com>


>Dan Ancona wrote:
>>
>> Anyway, the gist I'm getting from this thread is that a rigorous
separation
>> of formatting from any purely generic or abstract markup in a given XML
>> file format is not strictly necessary.  In fact, it could even be
>> beneficial in some circumstances and for some formats.  Correct?
>
>Personally I've come around to a pragmatist position on this, after some
>time as a radical Free The Text purist

If we subdivide the logical/presentation split we can come up with
the following 6 subdivisions:

    topical structures  (e.g.  <dog>)
    editorial structures  (e.g. <p> )
    characters
    glyphs
    page objects  (e.g. a line)
    layout structures (e.g. a column)

If there is a straightforward flow of dependence and synchronization
between these different structures, then is possible to start at the
topic structure and format all the way down to the layout (i.e. starting
from a higher and piggybacking the settings of the lower based on the
higher ones.)  This is the underlying model of, e.g. CSS & DSSSL
to a great extent: in DSSSL there is no feedback from the layout
program to the stylesheet language.

However, there are many kinds of documents where the flow of dependence
is not one-way or straightforward. For example, in a magazine the page
layout
determines how many characters a heading sould have, and in some designs
it might determine what kinds of editorial structures are possible

I came across an extreme example in a loose leaf system: the writers of
a prose section knew they had a fixed space to work in, but this could not
be determined at authoring time. So they wrote knowing that the last
paagraph might be deleted by the pagination system if it could not
be fitted. This is a case where the layout structure determined the
page-objects which determined which editorial structures made it into
the final publication.

Developers should be aware that if their publication requires more than
just a straight-forward flow of dependence between the various structures
(which are concurrently present in their publication) they may have to
spend a lot more development effort. A simple flow of dependence with
no reverse feeding back is easier to implement.


Rick Jelliffe

"The XML & SGML Cookbook" Prentice Hall, out in May 1998


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