XSchema Question 3: Internal/External subsets

Paul Prescod papresco at technologist.com
Wed Jun 3 15:23:55 BST 1998

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.

> This is obviously required for
> firewalls, but could also be valuable if the implementation language in the
> src= file could vary (e.g. Perl, Java). Of course it shouldn't act as a
> pseudo-stylesheet mechanism.

I'm not sure that implementation language is the crucial factor. Schemas
will hardly ever be full computer programs, and I would be worried about a
system in which the exact same schema is expressed in two different
languages (especially two different programming languages!). I think that
Rick is referring to different levels and types of schemas...one for
validating the parse tree, one for advanced hyperlinks, one for
knowledge-representation assertions (e.g. RDF Schemas) etc.

The namespaces proposal requires us to choose a single schema as the
"canonical" one as if all of the other levels and types of schemas were
somehow less important.

 Paul Prescod  - http://itrc.uwaterloo.ca/~papresco

Three things are most perilous: Connectors that corrode
Unproven algorithms, and self-modifying code

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