values in constraint_type col of dba_constraints

Hello everybody,

   I was looking at the values of constraint_type column of table dba_constraints:
I got

value          Meaning(That's what I think they might mean )
P          ->         Primary Key
U          ->         Unique
R          ->         ?
V          ->         ?
C          ->         ?

 Do you know what these values mean. Are there any more abbrevations that this column could hold and what they mean? Thanks,
Rajiv.     Received on Wed May 21 1997 - 00:00:00 CDT