Je t'invite fortement à lire la FAQ de Ronald Bourret sur les namespaces, tu y trouveras la réponse à ta question et bien pllus encore:
The URIs used as XML namespace names are not guaranteed to point to schemas, information about the namespace, or anything else -- they're just identifiers. URIs were used simply because they're a well-known system for creating unique identifiers. Don't even think about trying to resolve these URIs. (For details, see question 12.4.)
http://www.rpbourret.com/xml/NamespacesFAQ.htm