tom关于oracle的connection, session, process的总结
    A connection is a physical circuit between you and the database.  A connection might be one of many types -- most popular begin DEDICATED server and SHARED server.
    Zero, one or more sessions may be established over a given connection to the database as show above with sqlplus.  A process will be used by a session to execute statements.  Sometimes
there is a one to one relationship between CONNECTION->SESSION->PROCESS (eg: a normal dedicated server connection).  Sometimes there is a one to many from connection to
sessions (eg: like autotrace, one connection, two sessions, one process). 
    A process does not have to be dedicated to a specific connection or session however, for example when using shared server (MTS), your SESSION will grab a process from a pool of processes in
order to execute a statement.  When the call is over, that process is released back to the pool of processes.