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Re: Basic namespace question

• To: Daniel Gresh <dgresh@l...>
• Subject: Re: Basic namespace question
• From: Philippe Poulard <Philippe.Poulard@s...>
• Date: Mon, 17 Jul 2006 18:22:26 +0200
• Cc: xml-dev@l...
• In-reply-to: <44BBB22E.6080208@l...>
• References: <44BBB22E.6080208@l...>
• User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.7) Gecko/20050511

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@l...: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       |
  -----------------------------
  http://reflex.gforge.inria.fr/
        Have the RefleX !

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