RE: [xsl] Combining HTML/FO StyleSheets ( Indirection/Abstraction Methods) - Non-Trivial

[Wendell Piez <wapiez at mulberrytech dot com>]

Peter,

My guess is that the approach you suggest, namely targeting an intermediate 
processed format that you can then take both to HTML and to XSLFO, thereby 
sparing you the headache of duplicating processing logic, will get more 
common as applications like yours get more mature.

Either XHTML as a source for FO, or FO as a source for HTML, have their 
shortcomings IMHO. Both an XHTML->XSLFO stylesheet and an XSLFO->XHTML 
stylesheet would pretend to be very generic stylesheets, i.e. useful on any 
XHTML or FO, but in practice I think issues of styling and the split 
between good screen display and good print layout, will make this very 
difficult. (There is probably somewhere an HTML backend for FO: this 
implements, in effect, one of these.) In theory, CSS could provide a common 
ground of display semantics in the two cases. But this would mean having a 
CSS-aware super-XSLT processor (haven't seen one yet), and also doesn't 
account for the probability that you don't really want your web pages to 
look just like the print in any case.

Going from a unified, pre-processed format into either terminal target 
format will make for a cleaner separation of source content, processed 
content (basically a "content view"), and format. In particular, targeting 
an initial format and then going through a more generic transform to the 
terminal format, may be nice for implementating "house style" types of 
applications, where diverse material is to be funnelled into a single 
look-and-feel.

Whether your architecture and performance requirements can tolerate the 
multiple transformations this implies, is of course a question not 
answerable in the general case.

Also keep in mind, however, that the designers of XSLT do seem to have 
anticipated this scenario in providing xsl:import. The idea is that your 
processing logic would be in a single stylesheet, which would be imported 
by either of the others. The processor then gets a single transformation to 
do, not two. Both xsl:call-template and xsl:apply-imports ought to be very 
useful there.

Cheers,
Wendell

At 09:22 PM 3/3/2002, Joshua K. wrote:
> >       After slaving way at the problem I'll discuss below and
> > coming up with
> > several non-working solutions, I was wondering "Do people create
> > intermediate markup languages to ease the generation of both HTML and
> > FO?" By this I mean do people generate and intermediate format (XML)
> > which has all of the complex processing completed, and then have
> > trivial conversion style sheets from that format to HTML or XSL:FO as
> > appropriate? ((Example: intermediate tag like <paragraph> -> <p> or
> > <fo:block> depending on the desired output format))

...

>Let's say I have report_html.xsl, report_fo.xsl and report_csv.xsl. One 
>partial solution I developed was to write a stylesheet that transformed 
>the report_html.xsl into report_fo.xsl. However, this was only a partial 
>solution because I still needed to tweak the individual files as HTML 
>doesn't require <fo:table-column> elements.
>
>With hindsight, one thing I would have changed is writing the 
>report_fo.xsl first as this is more detailed, and then writing the 
>stylesheet to transform it to report_html.xsl. In one sense, this is using 
>XSL-FO as the intermediary format you mentioned. With the XSL-FO you can 
>either generate the PDF, or generate the HTML.


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Wendell Piez                            mailto:wapiez@mulberrytech.com
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