XSchema Question 3: Internal/External subsets

Peter Murray-Rust peter at ursus.demon.co.uk
Wed Jun 3 20:13:16 BST 1998

At 08:54 03/06/98 -0400, Paul Prescod wrote:
>Peter Murray-Rust wrote:
>> My understanding is slightly different. The ns= is used to formalise the
>> uniqueness and the 'ownership' of the namespace, e.g. xml.org.cml might
>> create a global identifier for CML. The src= field does not necessarily
>> have to point to the same document globally. 
>I'm not sure what you mean here. A particular namespace declaration will
>have zero or one srcdef, no matter where on the web it is accessed from.
>Rick's point is that it should allow zero or more.

I agree that a particular document can only have 0/1 srcDefs. However what
I meant was that two documents using the same namespacename (ns=) might
have different SrcDefs. In a trivial case this might be that one was a
mirror of the other (e.g. behind a firewall). However it also seemed
possible that there were functionally equivalent schemas (or perhaps even
non-equivalent ones) that different documents could choose. One reason - as
I hinted might be that the schema had to reference functionality expressed
in a computer language and that people might wish to use different languages.

Thus sites forbid Java but allow JavaScript (I make no comment on this
policy). I can see that site 1 might use:
<?xml:namespace ns="http://foo.com" prefix="F" src="http://foo.com/java/lib"?>
while the other one might use
<?xml:namespace ns="http://foo.com" prefix="FOO"

This may also be constrained by the availability of various packages. For
example, if you get a certain type of functionality in a file (e.g. a
mathematical formula) you may not have a choice about your symbolic algebra
package. This will also be true of chemistry. There will be a grey area
between schemas and stylesheets, especially if processing is required.


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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