Deepak Rajumar

 Profile Answers by Deepak Rajumar 

• Feb 18th, 2008

 

Facts are tables that refer to the dimension tables for details. Facts always hold the foreign keys. Grains are the maximum possible information that can be derived and the maximum possible level of information that can be derived or prodicted form any dimension.please let me know if you have any other option.

aniban

 Profile Answers by aniban 

• May 10th, 2008

 

Deepak's answer is correct - just rewording the way I see it. Grain of the fact table represents the most granular information you can get from that table. Typically it is the combination of the different dimensions present in the fact table. So, if you have a revenue table with store_id, product_id, customer_id, date_id as dimension and $ value and qty as facts, the grain of this table is per store per product per customer per day.

AVRKAM

 Profile Answers by AVRKAM 

• Jan 3rd, 2010

 

This is about granularity. that is, what level of data detail should be made avaialble in the dimension model. A reference to ATOMIC DATA has to be made here.

Atomic data is the most expressive data and should be the foundation for the fact table.

It is the most detailed information collected and such data can not be sub-divided further.  It is highly dimensional.

The more detailed and atomic the fact measurement , the more things we know for sure.

It provides maximum analytic flexibility, because it can be constrained and rolled up.

Anindya1281

 Profile Answers by Anindya1281 

• Apr 14th, 2010

 

In simple words grain can be considered as the lowest level in which you can store data in a table for example you want to store daily sale of a product and you have different stores so store_id and day would be at lowest grain

Advantage: You can always role up to showdata for higer grain for example in a city (if city has multiple store).

Disadvantage: To consumes more space

No if you add another attribute (like colour) to your table then the grain of the table changes, so proper care should be taken to determine what is the lowest level of reporting that needs to be done on the table to decide the grain.