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Namespace URLs

 
Greenhorn
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I don't understand what a namespace URL is supposed to point to. Is the namespace URL supposed to contain some kind of list of valid elements, data types, etc? I visited the XML Schema namespace URL (www.w3.org/2001/XMLSchema")and didn't see anything like that.
I have read the chapter in Professional XML that talks about namespaces, but found it to be very poorly done and only gave me more confusion.
I guess what I don't understand is when an XML parser sees a namespace declaration, does it actually go to that URL? If so, what does it do there, and what if that URL is offline?
Thanks.
 
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Jeff,
‘XML in a nutshell’ (page 64) says –
“Namespace URIs do not necessarily point to an actual document or page. In fact, they don’t have to use the http scheme. They might even use another protocol, such as mailto, in which URIs don’t even point to documents. ... The W3C got tired of receiving broken link reports for the namespace URIs in their specifications, so they added simple pages at their namespace URIs."
Cheers,
Dan
 
Jeff X Williams
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If a namespace is nothing more than a unique prefix, why do they generally include http://
Why not just www.something.com/namespace?
Are there cases when there is something actually located at the namespace URL? If so, what?
 
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