Tables in qlikview are denormalised.......
First of all what is normalization
Normalization---Normalization is generally used in relational database for reducing the redundant(repeated) and consistency.It i used to organize data.for example when you are using Employee table with the address table ,when you want to see the address,same as for city ,and other fields.
Some of disadvanatge of normalization are...
1>It is slow
2>The more your data is normalized the more are the no of joins
3>When we use denormalization we don't have to write complex queries.
That is why we prefer denormalization