let dbms_of_xml = function
    Xml.Element
      ("li",_,
       [Xml.Element("tuple",_,
                [
                  Xml.Element ("ti",_,[db]) ;
                  Xml.Element ("ti",_,[col]) ;
                ]
               )
       ]
      ) ->
        let db = db_of_xml db in
        let col = coldbms_of_xml col in
        (db, col)
  | e ->
      fail e "dbms_of_xml"