help understanding namespace

[XSLTnewbie 0]

I see this kind of declaration a lot in XSL files:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

and I tried opening the address referred to in the above declaration (http://www.w3.org/1999/XSL/Transform), and it's just a regular webpage, not some kind of collection of commands or syntax like I expected. my questions are:

1. how is this possible? how does machine understand commands like xsl:value-of if there's no specific codes in that URL?

2. what would happen if w3.org is down? will all web service that uses this namespace blow up?

 

and in the web service XML message, the structure is like so:

<foo:concat xmlns:foo="http://ttdev.com/ss"><s1>abc</s1><s2>123</s2></foo:concat>

let's say ttdev.com is a domain name I purchased (I put my web service in that server). and let's say for some reason, I change the domain name to myservice.com (switch to cheaper provider, etc.), does this mean the above message will blow up when trying to access my service which is now located at myservice.com? thanks a lot

[justsomeguy 1,135]

The URL is basically used as a unique namespace name, the browser or server doesn't actually connect to that URL to download anything. There's some more information here:

 

http://www.oracle.com/technetwork/articles/srivastava-namespaces-092580.html

[XSLTnewbie 0]

I also have trouble understanding the difference between qualified and prefixed elements:

<schema xmlns=”http://www.w3.org/2001/XMLSchema”targetNamespace=”http://www.example.com/name”xmlns:target=”http://www.example.com/name”>

and this one:

<xs:schema xmlns:xs=”http://www.w3.org/2001/XMLSchema”targetNamespace=”http://www.example.com/name”xmlns=”http://www.example.com/name”>

what's the difference? I only see that schema is prefixed, but name is not in the latter. what are the effects if I choose one over the other?

 

also this:

<name xmlns=”http://www.example.com/name”><first>John</first><middle>Fitzgerald</middle><last>Doe</last></name>

the example said that the elements (first, middle and last is qualified). I'll just assume that that would mean they won't get mixed up with other <first> element that belongs to other vocab.and also, is this what you call default namespace?

<n:name xmlns:n=”http://www.example.com/name”><n:first>John</n:first><n:middle>Fitzgerald</n:middle><n:last>Doe</n:last></n:name>

now this one is a bit weird. why do you need to prefix all the elements when previous example already qualifies the elements that belong to "name" vocab?

thanks

[justsomeguy 1,135]

 

 

what's the difference? I only see that schema is prefixed, but name is not in the latter. what are the effects if I choose one over the other?

The second one creates the xs namespace, the first one doesn't have a namespace prefix.

 

 

 

I'll just assume that that would mean they won't get mixed up with other <first> element that belongs to other vocab

They won't get mixed up as long as there aren't multiple vocabs in the same file. If there are, then you need to use namespaces to separate them, that's really what namespaces are for. Namespaces are a concept in languages other than XML, they are used to separate different pieces of code that might share names. They avoid naming conflicts when everything is in the same namespace.

 

Those examples are just illustrating the concepts, but they aren't all that useful on their own. With the last example, you wouldn't need to use a namespace if that was the only thing in the file.

[XSLTnewbie 0]

what's the difference between

<n:name xmlns:n=”http://www.example.com/name”><n:first>John</n:first><n:middle>Fitzgerald</n:middle><n:last>Doe</n:last></n:name>

and

<n:name xmlns:n=”http://www.example.com/name”><first>John</first><middle>Fitzgerald</middle><last>Doe</last></n:name>

[justsomeguy 1,135]

Well, one of them has the namespace prefix. That's only going to matter if it's in a larger file that uses the same element names in a different namespace.

[XSLTnewbie 0]

thanks for the reply justsomeguy, but I still don't quite understand yet. Could you please give me an example? thanks heaps

[justsomeguy 1,135]

If you have a single XML file that uses multiple namespaces, and every namespace has a "name" element, then you need to prefix every name element with the namespace that it belongs to. Otherwise it wouldn't know which name element you're referring to, it could be the name element from any of the namespaces. You specify the namespace to remove ambiguity.

[XSLTnewbie 0]

sorry, you lost me there. are we still talking about the <first> and <middle> and <last> element here? I was confused whether to add prefix to <first>, <middle> and <last> if it's contained in a prefixed element <name> like shown below:

<n:name xmlns:n=”http://www.example.com/name”><first>John</first><middle>Fitzgerald</middle><last>Doe</last></n:name>

and if I do, what's would the effect be if I dont add prefixes to <first>, <middle> and <last> element?

Thank you so much.

[justsomeguy 1,135]

From what I understand, you only need to prefix elements with a namespace if they are going to conflict with other elements from other namespaces. If you're dealing with a single XML element with a single namespace like you're showing then I don't think you need the prefix at all.

[XSLTnewbie 0]

<hn:husbandname xmlns:hn=”http://www.example.com/name”><first>John</first><middle>Fitzgerald</middle><last>Doe</last></hn:name><wn:wifename xmlns:wn=”http://www.example.com/name”><first>Jane</first><middle>Fitzgerald</middle><last>Doe</last></wn:name>

how about this one then? do I need to prefix the <first>, <middle> and <last> elements? and if I do, whose elements should I prefix? the husband, the wife or both, or neither?

thanks

[justsomeguy 1,135]

You would want to prefix them if you want to do things like look up all husband first name elements. If there was no prefix then asking for first name elements would return all of them.

[XSLTnewbie 0]

in what case would asking for a first name be returning all the first names? I'm only familar with xslt, so even without the namespace for husbandname and wifename element, I'll be able to access using "/husbandname/first" XPath expression. Am I missing something here? thanks

[justsomeguy 1,135]

If you just ask for each "first" element then it's going to return all of them regardless of the namespace. If that's not what you want to do then you need to use a namespace.

[XSLTnewbie 0]

ok, could you please show me some example where I do need namespace? thanks

[justsomeguy 1,135]

Check this article:

 

http://msdn.microsoft.com/en-us/magazine/cc302166.aspx