public Parser relativeKeyClause() {
        if (relativeKeyClauseParser == null) {
           FutureParser future = scoped("relativeKeyClause");
           relativeKeyClauseParser = future;
           future.setParser(
               sequence(
                   token("RELATIVE"),
                   optional(
                       token("KEY")
                   ),
                   optional(
                       token("IS")
                   ),
                   recordKeyDefinition()
               )
           );
        }

        return relativeKeyClauseParser;
    }