Slowly changing dimension applies to some cases where 
attribute for a record varies over time.

For example a person called narmatha lived in one place 
(india). So the original entry in the customer lookup table
like : customer id :100 name: narmatha country:India

At a later the person moved to UK
 
How should XYZ Inc. now modify its customer table to 
reflect this change? This is the "Slowly Changing 
Dimension" problem.

Slowly changing dimensions(SCD) is the type of dimensions 
which  changes with respect to time or peeriod.

Fo s ex: there is an table which has objects like 
Country City Employeeid ddress .

Here for example the say the employee of employee id say 
e23321 is presently in  Hyderabad after a month he is re-
located in Banglore than we can say the address dimension 
is SCD w.r.t. time

We have 3 types of SCDs:
SCD-1
SCD-2
SCD-3
SCD-1:where no historical data is not maintained only 
present data is maintained
SCD-2:Where complete historic + presentl data is maintained
SCD-3:Where one time historic(say previous) data+ current 
data is maintained