The USE statement specifies Declarative procedures to handle
  input/output errors and database exception conditions.  It can also
  specify procedures to be executed before the program processes a
  specific report group.

  Format 3 -

   USE [GLOBAL] FOR DB-EXCEPTION [ON { {DBM$_exception-condition} ... }].
                                 [   { OTHER                          }]

1 - DBM$ exception-condition

  is a symbolic constant name beginning with the characters "DBM$_".
  It identifies a DBMS exception condition.