Specifying validation routines
When you specify a validation routine for a table, the routine is loaded on demand during operation.
About this task
You can add a validation routine to an existing table, but the routine is not invoked to validate data that was already in the table.
Procedure
To
specify a validation routine for a table:
Issue the CREATE TABLE or ALTER TABLE statement with the
VALIDPROC clause. 
You can specify the VALIDPROC clause on a table that is activated with row and column access control. The rows of the table are passed to these routines if your security administrator determines that these routines are allowed to access sensitive data.
You can cancel a validation routine for a table by specifying the VALIDPROC NULL clause in an ALTER TABLE statement.