Compound Documents - necessary for success?

[Mark Birbeck]

Chris von See wrote:
> [snip on Ron Bourret's comments on how to use two DTDs in the same XML
document]
> I may be showing my gross ignorance of both XML and namespaces here,
but
> isn't this at least part of the problem that namespaces were meant to
> address?

In response Ronald Bourret wrote:
> Nope -- no ignorance at all.  This is very definitely the problem 
> namespaces were meant to address.

Well, sort of. But note that you can use namespaces even without using a
DTD. A standalone document that is well-formed might still want to have
the following, in order to provide clues to any application that is
processing it:

    <xml xmlns="uri:mybits" xmlns:dt="uri:datatypes">
        <person>
            <name dt:type="string">Fred</name>
            <contract type="short-term" />
            <hair type="greasy" dt:type="string">blonde</hair>
        </person>
    </xml>

In this example, if the application was going to process 'type' in a
certain way (say an XSL processor), then it needs the namespaces to help
it work out which 'type' is which. Also, if the namespace wasn't there,
then you wouldn't be able to use both 'type' attributes in the same
element. But note that no schemas need be involved.

Conversely, if you devise a DTD that uses another DTD, you don't
necessarily need to use namespaces. In the height/player example given
before there is no ambiguity, so why would you introduce a namespace?

So, back to compound documents. I think as a stop-gap you need dynamic
DTDs. Just as many features of XML are best implemented using dynamic
documents generated from databases, why not generate a top-level DTD
that contains whatever lower level DTDs it needs to define the relevant
compound XML document? The top DTD would include some basic stuff for
containing a list of documents, and then include whatever other DTDs it
needs for each document in turn.

Mark Birbeck
Managing Director
Intra Extra Digital Ltd.
39 Whitfield Street
London
W1P 5RE
w: http://www.iedigital.net/
t: 0171 681 4135
e: Mark.Birbeck at iedigital.net


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