Returns a web accessible URL for the resource.
This function should return a URL that can be embedded in a web page and accessed from a browser. For example, the external URL of "youtube://xIpLd0WQKCY" might be "http://www.youtube.com/watch?v=xIpLd0WQKCY".
Returns a string containing a web accessible URL for the resource.
public function getExternalUrl();