All,
Added URIs as URIs are not URLs. Yes, a URL can be a URI :-)
In a nutshell the Web provides access by reference to things that are
not always resources such as documents, images, and other files. You
can also reference abstract things such as People, Music, Places,
Events, and many other real world things. To do this you must be able
to explicitly identify a Person and a Document or File as separate
things which is what HTTP based URIs deliver withing the context of
the Web. Of course, a Document or File URL can server as a URI for a
Document or File, but this cannot be so for a Person, Place, or other
abstract thing mentioned in a document etc..