Only one flow line should come out from a processsymbol.
只有一个流线应该从一个进程的象征。
2
If it finds a match, it USES the send operator (the! Symbol) to send a message to the broker process telling it to place an order.
如果匹配上了，就用发送操作符(即！符号)向broker进程发送一则消息，告诉它下单。
3
The third (right-most) rectangle, named BookRoom, has both a human and a plug symbol, which means a user performs part of this activity and the rest is done by some automatic process at the back end.