URI, URN and URL. Still confused after RFC 3986
I am still confused about URIs and URLs after reading RFC 3986 1.1.3 (via RAW).
Can http: URIs be used to identify non-digital objects? The W3C clearly thinks so: the namespace for this code is identified by the URI http://www.w3.org/1999/xhtml.
But the same string is the URL for an HTML page.
Quoting RFC 3986:
The term "Uniform Resource Locator" (URL) refers to the subset of URIs that, in addition to identifying a resource, provide a means of locating the resource by describing its primary access mechanism (e.g., its network "location").
My problem: The web page and the namespace are different resources. Something is located on the network, but that something is not the resource identified by the URI. The difference will be more obvious if the URI http://ships.reg.fo/FD/530 identifies a ship. Whatever you access by the link http://ships.reg.fo/FD/530, it will not land some 20 tons of ship on your desk.
Still, I find it very useful that http://www.w3.org/1999/xhtml describes the object identified by http://www.w3.org/1999/xhtml. Otherwise, we'd have to google for pages with DC:subject="http://www.w3.org/1999/xhtml". But the RFC says the resources identified and accessed are the same, it does not allow for accessing the metadata of the identified resource.
One possibility might be placing the HTML description at http://www.w3.org/1999/xhtml.html, and make http://www.w3.org/1999/xhtml redirect there. But even a redirect is a resource, and a redirect is certainly not a namespace.
I have to correct myself. When used to identify a namespace, "http://www.w3.org/1999/xhtml" is NOT a URI. It is, due to the context, a NAMESPACE identifier. The URI "http://www.w3.org/1999/xhtml" is identifying a certain XHTML page, and nothing else.