RE: [xml-dev] Basic namespace question

["Chiusano Joseph" <chiusano_joseph@bah.com>]

Also, to answer the following:

> Is information from that URI being used in the XML document somehow?  

Although it could/should be (if it is indeed a resolvable URI), that is not a requirement. For example, if you use a URI of 'http://ecommerce.org/schema' per your example below, chances are that the information in the XML document somehow relates to e-commerce (it would be a good, logical bet). This not have to be the case, but it seems like good practice to me to have such an association. If your URI were more specific, perhaps to indicate a certain domain (such as "automotive"), then chances are that the information in the XML document somehow relates to automotive e-commerce, perhaps the purchase of auto parts.

Joe

Joseph Chiusano
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-----Original Message-----
From: Philippe Poulard [mailto:Philippe.Poulard@sophia.inria.fr] 
Sent: Monday, July 17, 2006 12:22 PM
To: Daniel Gresh
Cc: xml-dev@lists.xml.org
Subject: Re: [xml-dev] Basic namespace question

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...") -à 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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--
Cordialement,

               ///
              (. .)
  --------ooO--(_)--Ooo--------
|      Philippe Poulard       |
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  http://reflex.gforge.inria.fr/
        Have the RefleX !

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