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Re: XSL intent survey

Subject: Re: XSL intent survey
From: David Carlisle <davidc@xxxxxxxxx>
Date: Fri, 20 Nov 1998 17:16:42 GMT
Re: XSL intent survey
> I probably don't know enough about
> document stylesheets to understand why you need the formatting objects
> and perhaps someone on the list can explain.

Because you want to specify the format of the output:-)

You are probably thinking in terms of HTML where there is some kind of
default formatting for a fixed set of elements (based on historical
actions of the browsers, mainly) and typically style sheets are used
just to tweak or fine tune those defaults.

For XML you don't have any default semantics, so if you want to say that
the content of a <p> element should be typeset as a paragraph you need
some way of referring to the abstract notion of a paragraph. That's what
the paragraph formatting object is. Similarly the other formatting
objects give the fixed set of `typographic' (may be rendered as speech
or braille or whatever) facilities that should be implemented.

It is rather sad that the `suggested' answers in this survey didn't
suggest the most obvious language on which to base this system (as it is
in fact the language on which large parts of XSL are based) namely
dsssl. (`base' can be taken rather loosely, for example people seem not
to like dsssl syntax (for (some (strange (reason))))).

DSSSL had two separate languages. A transformation language and a style
language. As far as I know the transformation part never got
implemented. The major reason why the non implementation of dsssls
transformation language has not turned out to be important was that
James Clark showed how one could effect transformations using the style
language (by having a set of flow objects that write SGML instances).
a dsssl flow object is more or less the same thing as an XSL formatting
object but in the current XSL draft this mechanism of using the same
paradigm to do both transformations and style is more cleanly expressed
than in dsssl (where it is a more or less non standard extension).

XSL has other problems (its transformations and patterns are not
powerful enough to say do anything with MathML), and it doesn't have many
of the needed formatting objects, but that does not worry me too much as
it is explicitly says in the draft that more will be added later.

Actually I can not see any use at all for having a style language that
can not do transformations. Given that you are going to have to
transform the original parse tree to produce the required output tree
for the formatting, why not just add the formatting characteristics as
you construct that tree (as you can do in a combined language) rather
than have to go over the tree again adding formatting characteristics
with a second style language?

David


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