Why do objects become invalid?

Hello,
I want to ask a question,
When I connect as system/mamanger and
SELECT * FROM ALL_OBJECTS WHERE STATUS = 'INVALID'; I can find some objetcs like procedures,triggers,views become INVALID. And if I recompile the scripts,the objects' STATUS become VALID. But I don't know why?
'Cause I don't alter the objects,but they become INVALID. Please give me more information about this. Please Cc to : violin.hsiao_at_mail.pouchen.com.tw,Thank you :-) Received on Tue Sep 15 1998 - 21:03:10 CDT