Confused with v$session and v$process

[Chuan Zhang]

Hi, DBAs,        I think that I might ask a simple question but I have been confused sometimes for a long time. Could someone help me to clarify these?     First, is " v$session.paddr=v$process.addr" the only way to join these two tables"     Second, I am confused about the Username, Osuser in v$session with the Username in v$process.   "select a.program, b.program,a.username,b.username,b.osuser from v$process a, v$session b where a.addr=b.paddr and sid in (18,33,68,115,144,150)" One of the results is as follows: a.program :oracle@vantive (TNS V1-V3) b.username:  iwserver@vantive (TNS V1-V3) b.username: oracle a.username: SWBAPPS a.username: vantive    Third: I am confused with Spid,pid in v$process and sid in v$session.  Is pid (oracle process id) oracle server process id? what is it used for? Thanks very much for your help. Chuan