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RE: [xml-dev] Basic namespace question

Hopefully this helps answer your URN questions:

http://www.w3.org/Addressing/rfc1737.txt 

Kind Regards,
Joseph Chiusano
Associate
Booz Allen Hamilton

700 13th St. NW, Suite 1100
Washington, DC 20005
O: 202-508-6514  
C: 202-251-0731
Visit us online@ http://www.boozallen.com

-----Original Message-----
From: Daniel Gresh [mailto:dgresh@lle.rochester.edu] 
Sent: Monday, July 17, 2006 12:51 PM
To: Philippe Poulard; xml-dev@lists.xml.org
Subject: Re: [xml-dev] Basic namespace question

Philippe Poulard wrote:

> hi,
>
> namespace URIs are used to disambiguish names used in elements (and 
> sometimes in attributes) ; the idea is to consider that a name has 2 
> parts, an ID and a local name ; 2 elements that have the same local 
> name are distinct when the ID you choose is not the same than mine ; 
> now what would happenned if unfortunately we have both choosen the 
> same ID ? we would have a clash ; the solution would be :
> 1) to disambiguish again our elements by considering that a name has 3 
> parts (an ID, another ID and a local name) ; now loop again if we 
> choose again the same IDs
> 2) to choose a better ID
>
> so we must ensure that when you choose an ID, it is not the same than 
> mine ; the idea is to use a "universal ID", an ID that is unique all 
> over the world
>
> candidates :
> -URIs ("http://foo.com/myNs"; or "urn:isbn:9-780201-770049") -GUIDs 
> (they are also expressible with URN : "urn:guid:etc...") - la Java 
> ("com.foo.myNs") -...
>
> URIs win
>
> avoid using "that text document" : even if XML processors won't 
> complain because it's not an URI string, it is not a unique string
>
> so, the kind of URI you could use could be something like this :
> "http://lle.rochester.edu/myProject/myNs";
> or
> "tag:dgresh@lle.rochester.edu:2006-07-17:myNs"
> or any other, as long as it is unique
>
> Daniel Gresh wrote:
>
>> I have a basic question about XML Namespaces, as I just cannot seem 
>> to fully grasp the concept.
>>
>> I know how to set up a namespace, and I know how they are used in the 
>> document and such; my question is mainly about the URI associated 
>> with a namespace. Let's use this as an example:
>>
>> |<x xmlns:edi='http://ecommerce.org/schema'>
>>  <!-- the 'price' element's namespace is http://ecommerce.org/schema 
>> -->  <edi:price units='Euro'>32.18</edi:price> </x>||
>>
>> Now I'm not too sure how to phrase this question, but here goes: do I 
>> have to associate a URI with a namespace? In the above example, what 
>> would be the case if there was no xmlns declaration and the ns "edi"
>> was used? I suppose what I am asking is: what is the benefit of 
>> declaring an xmlns in the manner  xmlns:prefix='URI'? Is information 
>> from that URI being used in the XML document somehow? It's all very 
>> confusing to me.
>>
>> Also, let's say I have a simple text document located somewhere on my 
>> hard drive, like C:\document.txt. If I wanted to define a namespace 
>> for that document, such as  xmlns:doc='that text document', how 
>> exactly would I do so? Is it even needed?
>>
>> Thanks in advance,
>> Dan
>> |
>>
>> -----------------------------------------------------------------
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>
>
Thanks everyone for the replies, I understand it much better now.

Just one last question:

Rather than using a URL, such as http://myDomain/myNamespace, how would I use a URN? URLs are self-explanatory to get to - i.e. they're easy to determine. However, how does one find or create a URN? If I have a URI, http://myDomain/myNamespace, that is the URL. However, how could I determine a URN for that? Is it possible?

Thanks agian,
Dan

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