Function returns the value.Trigger is not complusory return 
the value.

Triggers: are special class of stored procedures to execute 
automatically when an update,insert or statement is issued 
against a table or view.
Function:Function is used to return value after performing 
the tasks to the callable fucntion.

PL/SQL has two types of sub programs
Function and Procedures.
A Trigger is a stored procedure which is implictly called 
by the oracle engine when an DML action is performed.
Trigger consists of three parts
A trigger statement
A trigger restriction
and the triggering action

Functions are different from procedures as
functions return value whereas procedure doesnt
To carry out set of tasks a certain pl/sql statements are 
grouped in a procedure.
After performing some tasks and returns the result(function)
functions are written explicitly by the user.