URIs identify and URLs locate (on network); however, locators are also identifiers.
So all URLs are URIs (actually not quite - see below), and all URNs are URIs - but URNs and URLs are different, so you can't say that all URIs are URLs.
URIs identify and URLs locate (on network); however, locators are also identifiers.
So all URLs are URIs (actually not quite - see below), and all URNs are URIs - but URNs and URLs are different, so you can't say that all URIs are URLs.