Query Protocols...

PICS provided a query mechanism for obtaining ratings from label bureaus:

GET /Ratings?opt=generic&
             u="http%3A%2F%2Fexample.com%2Fmayhem"&
             s="http%3A%2F%2Fwww.w3.org%2F2004%2F05%2F07-CS-RDF%2Fv2.5"
             HTTP/1.0