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   Re: XSchema Spec Section 2.2, Draft 1

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  • From: Peter Murray-Rust <peter@ursus.demon.co.uk>
  • To: "Michael Kay" <M.H.Kay@eng.icl.co.uk>,"XML Dev" <xml-dev@ic.ac.uk>
  • Date: Thu, 25 Jun 1998 04:27:41

At 20:05 23/06/98 +0100, Michael Kay wrote:
>>Peter Murray-Rust wrote:
>>> Unless there is
>>> sensible running text whose prime purpose is to be read
>by humans there is
>>> no particular value in having mixed content (i.e. strings
>+ elements mixed).

I probably didn't mean to make it sound so black and white :-)
>Counter-example from GedML (adapted to make it
><NAME>Frederick BLOGGS
>   <SOURCE>Birth Certificate</SOURCE>
>        <ON>12 Jan 1983</ON>
>        <BY>MHK</BY>
>   </CHANGED>
>   <NOTE>Generally signed himself "Frederik"</NOTE>
There's nothing wrong with this, of course.

My own style would be to wrap 'Frederick Bloggs' into an element. In
implementation terms I have implemented PCDATA as a sort of second-class
element - i.e. it gets displayed differently in JUMBO, etc. Methods of
linking to it are different. Perhaps I'm wrong here.

>Unfortunately I am unable to declare in the DTD that the
>element contains "PCDATA content followed by zero or more of
>the following child elements", XML's peculiar rules mean
>that with mixed content I cannot declare any ordering or
>cardinality constraints. (I wonder if someone thought that
>there was no requirement?)

It was to avoid the problems of pernicious mixed content, I believe.

Remember also that:
<SOURCE>Birth Certificate</SOURCE>
        <ON>12 Jan 1983</ON>
   <NOTE>Generally signed himself "Frederik"</NOTE>

is a valid instance of a document against your DTD. The person's name is
then &#13; or something similar


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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