question on Call.setTargetService(String)

[yong fu]

Hi, all:

The following code does not work unless I insert "setTargetService(String)"
line.

------------------------
call.setTargetEndpointAddress(url);
call.setRequestMessage(new Message(Obj, true));
call.setTargetService("Any string here");                 //won't run
without it.
call.invoke();
-----------------------

Since I can use any string for this setTargetService call,   the question is
what is
this TargetService used for?

thanks,

Yong