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   Re: [xml-dev] Is a namespace a set?

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 From: "Klaus Backert" <KlausBackert@compuserve.com>
> ;-) Is a namespace a set or not? Does it depend? Does it matter?
An XML namespace is a collection of names (a vocabulary).
A XML namespace has a URI.
A URI identifies a WWW resource.
A WWW resource may have one or more retrievable entities.
No-one can agree what should be retrievable.
But a URI is a useful thing. 
So RDDL provides one answer. 

An XML schema has symbols in a "symbol space".
These "symbols" are names in XML namespaces but potentially qualified by their
parent element. These are sometimes called "local elements" versus
"global elements".  For example, an element X could have a complex
type definition in which contains local element declarations for an element X.

So a name in a namespace does not always have a 1:1 association with
a particular schema definition. Similarly, the elements in a whole namespace
may be used in different ways by different schemas which use elements
from the namespace. 

But often there will be one general or typical schema for a namespace.
Yet variants can be expected over time due to maintanance, etc.  

So a namespace may be a set, but that does not mean an element
in a particular namespace will always have the same content model

Rick Jelliffe


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