What is the difference between Star Schema and Snow Flake Schema in Qlikview?

qlikview

#1

Hi,

I am preparing for Qlikview Interview and I have noticed that the difference between Star Schema and Snow Flake Schema is one of the common question. Can you help me to understand it better?

Thanks


#2

Hi,

Star and Snowflake Schema are the two data models in qlikview.

Star Schema has single fact table connected to dimension tables and it visualize as a star. In star schema only one link establishes the relationship between the fact table and any of the dimension tables.

Snowflake Schema is an extension of the star schema. In this model, dimension tables are not necessarily fully flattened. Here, very large dimension tables are normalized into multiple sub dimensional tables. It is used when a dimensional table becomes very big. Also, every dimension table is associated with sub dimension table and has multiple links.

The main difference between star schema and snowflake schema is that

  • The star schema is highly denormalized and the snowflake schema is normalized. .
  • Performance wise, star schema is good but if we think about memory then snow flake schema is better than star schema.
  • A dimension table will not have parent table in star schema, whereas
    snow flake schemas have one or more parent tables.
  • Snow Flake Schema has bottom-up appraoch where as Star has Top-down.
  • Star Schema has fewer joins and Snow flake has higher

Hope this helps!

Regards,
Sunil