The RDB$CONSTRAINT_RELATIONS system table lists all tables that
    participate in a given constraint. The following table provides
    information on the columns of the RDB$CONSTRAINT_RELATIONS system
    table.

                                Data
    Column Name                 Type      Summary Description

    RDB$CONSTRAINT_NAME         char(31)  The system-wide unique name
                                          of the constraint.
    RDB$RELATION_NAME           char(31)  The name of a table
                                          involved in the constraint.
    RDB$FLAGS                   integer   Flags.
    RDB$CONSTRAINT_CONTEXT      integer   The context variable of
                                          the table involved in the
                                          constraint.
    RDB$SECURITY_CLASS          char(20)  Reserved for future use.