Sometimes, it is necessary for programmers to name and trap their own exceptions - ones that aren't defined already by PL/SQL. These are called Named Programmer-Defined Exceptions.
The syntax for the Named Programmer-Defined Exception in a procedure is:
CREATE [OR REPLACE] PROCEDURE procedure_name
[ (parameter [,parameter]) ]
RAISE exception_name ;
WHEN exception_name THEN
WHEN OTHERS THEN