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RE: Can XML Schemas do this?

• To: "Paul Prescod" <paul@p...>
• Subject: RE: Can XML Schemas do this?
• From: "Joshua Allen" <joshuaa@m...>
• Date: Tue, 21 Jan 2003 12:11:10 -0800
• Cc: "Eric van der Vlist" <vdv@d...>,"Jeff Lowery" <Jeff.Lowery@c...>,"Bryce K. Nielsen" <bryce@s...>,"xml-dev" <xml-dev@l...>
• Thread-index: AcLBh5HBz+E/O9OlRAiGFuLOLzaE/wAATzpg
• Thread-topic: Can XML Schemas do this?

That makes sense.  Attributes are unsuitable for some scenarios, but for
most cases I agree.  Personally, I would like to see schemas that allow
attribute ordering as well, so that streaming processors could take
advantage of that too :-)

> -----Original Message-----
> From: Paul Prescod [mailto:paul@p...]
> Sent: Tuesday, January 21, 2003 11:59 AM
> To: Joshua Allen
> Cc: Eric van der Vlist; Jeff Lowery; Bryce K. Nielsen; xml-dev
> 
> Joshua Allen wrote:
> > ...
> >
> > That's an interesting point.  I think the "user perspective"
argument
> > becomes more difficult to back up when you have element content that
> > involves lots of optional children -- in those cases the user often
> > wants to be able to insert whichever elements matter without
necessarily
> > worrying which order they come in.
> 
> I find that these are most often handled by attributes. Probably part
of
> the tension in this discussion comes from people who have a natural
> aversion to attributes trying to use elements as attributes.
> 
> > ... Imagine for example if command-line
> > apps were written to expect a certain order to command-line
arguments.
> > It would certainly save people from having to write getopts.c, but
would
> > actually be an *impediment* to usability and user expectations.
> 
> IMO, the usability problem with command lines is that sometimes
options
> are order sensitive and sometimes they are not. XML makes a clear
> distinction: attributes are not order sensitive. Elements are. Except
> when they aren't. Eric and others in this thread are arguing for the
> "except when they aren't" becoming more common.
> 
> Another argument in favour of enforced ordering: decent XML editors
will
> insert the required elements in for you in the right order. But they
> can't if order isn't enforced, because they don't know what order the
> author wants. That's the irony of this discussion...we're saying
"order
> doesn't matter therefore force the user to choose it."
> 
> If you spend a little time in a decent XML editor you'll probably find
> that enforcing an order does the user a favour by letting their tool
> help them better. On the other hand, attributes are usually ideal for
> the cases where order REALLY DOESN'T matter and the XML editor will
> convey this by presenting the attributes in alphabetical order.
> 
> > There are some scenarios where order naturally matters, and others
where
> > the user *assumes* it will matter, but I think there are plenty of
other
> > cases where users would be unpleasantly surprised by finding that
order
> > matters.
> 
> Most of these can be handled with attributes. In a few cases the
> limitations of attributes are really a problem but more often people
> avoid them out of a minimalist distaste for an "extra feature." If XML
> had structured attributes this whole discussion would go away.
> 
> Anyhow, the nature of the original question makes me nervous. We
aren't
> talking about a content model of the form:
> 
> <!ELEMENT x (a? & b? & c? & d? & e?)>
> 
> As I understood it, he wants more complex content model particles in
the
> options (that's why xsd:all isn't good enough). In my opinion, the
> resulting content model is going to be quite confusing. XSD's
> limitations may be arbitrary but IMO, they are (accidentally) pointing
> him towards better content model design.
> 
>   Paul Prescod
> 

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