can u explain one critical mapping? 2.performance issue which one is better? whether connected lookup tranformation or unconnected one?

it depends on your data and the type of operation u r doing.
If u need to calculate a value for all the rows or for the maximum rows coming out of the source then go for a connected lookup.Or,if it is not so then go for unconnectd lookup.Specially in conditional case like,
we have to get value for a field 'customer' from order tabel or from customer_data table,on the basis of following rule:
If customer_name is null then ,customer=customer_data.ustomer_Id
otherwise customer=order.customer_name.
so in this case we will go for unconnected lookup

      
Dimesions are
1.SCD
2.Rapidly changing Dimensions
3.junk Dimensions
4.Large Dimensions
5.Degenerated Dimensions
6.Conformed Dimensions.