Protocol buffers supports optional, required and repeated fields. An example of an address bookmessage definition using protocol buffers would look like this.
Protocol buffers支持可选的，必需的和重复的字段。
2
"The Power of Pull" is a book with a serious message.
《轻拉一把亦有力量》书中带有一系列的信息。
3
Or possibly it fires more than one response message to the client as we see in the book ordering process, where one message confirms the order, another message indicates dispatch of the order.