def create_connection(self, id_scope=IdScope()):
        from vistrails.core.vistrail.port import Port
        from vistrails.core.modules.basic_modules import identifier as basic_pkg
        source = Port(id=id_scope.getNewId(Port.vtType),
                      type='source', 
                      moduleId=21L, 
                      moduleName='String', 
                      name='value',
                      signature='(%s:String)' % basic_pkg)
        destination = Port(id=id_scope.getNewId(Port.vtType),
                           type='destination',
                           moduleId=20L,
                           moduleName='Float',
                           name='value',
                           signature='(%s:Float)' % basic_pkg)
        connection = Connection(id=id_scope.getNewId(Connection.vtType),
                                ports=[source, destination])
        return connection