let type_sql_of_xml = function
    [ Xml.Element("ti",_,[Xml.PCData t]);
      Xml.Element("ti",_,[s1]);
      Xml.Element("ti",_,[s2]);
    ] ->
      (unescape t,
       opt_of_xml string_of_xml s1,
       opt_of_xml string_of_xml s2)
  | e -> fail (Xml.Element ("list",[],e)) "type_sql_of_xml"