words (RE: extensibility in XSchema?)

Peter Murray-Rust peter at ursus.demon.co.uk
Thu Jun 25 06:20:04 BST 1998

I think Rick and I are on the same wavelength

At 00:25 24/06/98 +1000, Rick Jelliffe wrote:
>> From: John E. Simpson
>> Peter, I think you've got a bootstrapping problem here (or an illustration
>> of Godel's theorem :). XML, like SGML, explicitly separates considerations
>> of presentation from those of content ("presentation" covering a whole
>> gamut of "things you can or should DO with this content"). It seems to me
>> that you're asking for some generic way of making the separation go away,
>> no? But shouldn't this be *impossible* under the very terms by which XML
>> makes its way in the world?

This [JES] is an interesting view - I see what you are getting at. That it
should be formally impossible to use XML to describe any actions or
implementations. I think is too purist. The Perl hackers out there (e.g.
me) don't and won't think this way and they will assume that XML has a way
of 'doing what they want'.

>No, because the processing instructions are just as much a part of XML (and
>SGML) as elements. In the early days of SGML there was a lot of polemic
>against PIs, to correct the prevailing RTF/TeX view--you can see from Steve
>N's recent comments that the concern to stop XML people from confusing
>generic markup with procedural markup is very strong still. Similarly there
>is still a reductionist view that we just need elements for everything: that
>PIs and entity references are impure or inelegant.
>There is a currently a way to bind a PI to an element:
><!ENTITY x "<?RJ take this and shove it ?>" >
><object  PI="x">A wooden horsey</object>

Wow! This is standard? in XML? If so, it requires a smarter bear than me to
dig it out of the spec :-). But - if all the SGML gurus say 'yes, of
course, we meant you to do that all along' great. But *please* let's have
it in some examples somewhere in big letters.

And, of course, if it's standard, I have to implement it. So when parsing I
have to think about whether an attribute is of type entity and all the
things it might do. Please can I have a list... :-)


>What Peter is asking, I think, is for some agreed on PI notation which can
>be used to launch particular applications, based on an attribute in them.
>This is no different than
>	<?xml:stylesheet href="www.blah/blah" type="application/java"
>	<?xml:stylesheet href="www.blort/blort" type="text/css" title="Simple" ?>
>But rather than just being limited to just stylesheets to be run in the
>current browser, he wants to be able to invoke other browsers.


>This is already under W3C consideration: see James Clark's note on
>stylesheets http://www.w3.org/TR/NOTE-xml-stylesheet.

Ah! If this is really on the way, and we can bind MIME types to
stylesheets, I suspect my problem is soluble. But we need to publicise it :-)


Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
net connection
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary

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