Materialized view : (How to update base table)

Experts,

We can updatable create materialized view by using FOR UPDATE clause but
Can we also update our master/base table when materialized view is updating?
If yes, how?

consider this syntax:

create materialized view mt_emp_20
build immediate
refresh complete on demand
for update
as
select scott.emp.empno, scott.emp.sal,scott.emp.ename,scott.emp.job
from scott.emp
where scott.emp.deptno= 20


Dear Expert,

I have created one materialized view and set time for refreshing. It has created one job for managing this activity but oracle does not run this job. Why?
If I run this job explicitly it runs perfectly. Then why is it not running automatically.

Syntax: (Refershing every 2 minuts)
create materialized view MT_EMP_40
refresh force on demand
start with to_date('12-10-2007 15:04:11', 'dd-mm-yyyy hh24:mi:ss') next sysdate + 1/1440*2
as
select scott.emp.empno, scott.emp.sal,scott.emp.ename,scott.emp.job
from scott.emp
where scott.emp.deptno= 40