Types of Triggers

A trigger can be a stored PL/SQL or C procedure associated with a table, view, schema, or the database itself. Oracle Database XE automatically executes a trigger when a specified event takes place, which usually is a DML statement being issued against the table.

You can create triggers to be fired on any of the following:

DML statements (DELETE, INSERT, UPDATE)
DDL statements (CREATE, ALTER, DROP)
Database operations (LOGON, LOGOFF)