涉及的dbms_pipe包中的过程和函数：
（1）PACK_MESSAGE Procedures
用途：Builds message in local buffer
（2）SEND_MESSAGE Function
用途：Sends message on named pipe: This implicitly creates a public pipe if the named pipe does not exist
（3）RECEIVE_MESSAGE Function
用途：Copies message from named pipe into local buffer
（4）UNPACK_MESSAGE Procedures
用途：Accesses next item in buffer