xml-dev - Re: XSchema Spec Section 2.2, Draft 1

[rbourret@dvs1.informatik.tu-darmstadt.de (Ron Bourret)]

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).
> >
> Counter-example from GedML (adapted to make it
> self-explanatory):
> 
> <PERSON>
> <NAME>Frederick BLOGGS
>    <SOURCE>Birth Certificate</SOURCE>
>    <CONFIDENCE>High</CONFIDENCE>
>    <CHANGED>
>         <ON>12 Jan 1983</ON>
>         <BY>MHK</BY>
>    </CHANGED>
>    <NOTE>Generally signed himself "Frederik"</NOTE>
> </NAME>
> 
> The general form is that the "attributes" of an object are
> represented by the content of a first-level child element,
> and qualifiers to the attributes (source, confidence level,
> alternative values, etc) are represented by grandchild
> elements.
>
> [snip]
> 
> 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?)

I must be missing something here, because I can't see any advantage to using 
mixed content here.  In fact, your inability to specify the format you want in 
your DTD is just another argument to avoid mixed data.  Why not just use the 
following content models, which you've probably already thought of?

   NameInfo (Name, Source?, Confidence?, Changed?, Note?, ...)
   Name (#PCDATA)
   Source (#PCDATA)
   Confidence (#PCDATA)
   ...

Given the messiness of storing mixed data in a database, I can't see why you 
would want to do it.  If you want to be able to mechanically separate what is a 
data-child (e.g. Name) and what is a metadata-child (Source, Confidence, etc.), 
you could throw the metadata-children into attributes or shove them down another 
layer.  Perhaps a better example?

-- Ron Bourret

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