What is Constraint type O ?

I niticed that there are contraint type O (other than P - Primary, U - Unique, F - Foreign ...)

TABLE_NAME                            Constraint type
------------------------------            ------------------
AQ$DEF$_AQCALL                   O
AQ$DEF$_AQERROR                O

Is this type used by Oracle system (not by users)? Thanks
Tom Received on Mon May 14 2001 - 20:48:56 CDT