How to choose the namespace name of a new XML language?

I've created a (domain-specific) language based on XML that I hope will be widely used. To "implement" it I'm using an xsd file.

Until now I've used an url like this as the xml-language namespace :

http://languagemainsite.org/lang/1.0/

Now, I'm not sure it's the best way to choose the namespace, for long term:

Maybe the version number in the namespace is overkill? It's already defined in the "version" attribute too, but I thought it would be nice to have different url per version?
Is it always good to use an url for this?
????

Any advice about naming namespaces for xml-based language?

Solution

If the foo element in the namespace http://languagemainsite.org/lang/1.0/ is semantically a different concept to a foo element in the namespace http://languagemainsite.org/lang/1.1/, the namespaces should be different. If they're not—if a Lang-1.1 foo is just a Lang-1.0 foo maybe with a few extra features—they should be in the same namespace.

Consider, for example, the <p> element in XHTML 1.0, XHTML 1.1 and XHTML5. It is semantically the same thing (a paragraph) in all versions of XHTML, so they can all live in the http://www.w3.org/1999/xhtml namespace, even though they have different capabilities in the different language versions.

Including a version number in the namespace makes backwards-compatibility very difficult. Applications supporting two versions of the language would have to switch namespaces to cope with the same named elements, and a version-1-supporting application can't practically read a version-2 document at all.

So only use versioned namespaces for new ‘major version’ updates that deliberately completely drop backwards compatibility. Otherwise, a version attribute on the root element is generally a better idea.

And yes, you should use a URL, in order to avoid clashing with others' namespaces. It's polite to put some descriptive information up at the URL you use.