Surrogate key is the dummy key which is used to allow the
duplicate values

Surrogate key is contigeous numbers generated by DB in a 
table which acts as a primary key since surrogate key has 
unique values.

for eg : 
101,102,103,104,105............ so onl

Surrogate Key is a primary key in datawarehousing, the only
difference between surrogate key and primary key is that
surrogate key allows duplicate values but not primary key.

Surrogate key is unique key which is used in type 2 
dimension.

When we transfer the data from the source to the target
tables i.e dimension tables,we will be having one primary
key for the dimension table,but in the scd type 2 will be
having the repetative data i.e history+current data,so we
will be using the surrogate key for the dimension tables for
identifying the 
rows uniquely this surrogate is implemented in the ETL
process by using the "Sequence Generator Transformation".

            The surrogate key will be act as primary key in
the scd type 2 and primary of dimension table will be the
natural key.