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What are Semi-additive and factless facts and in which scenario will you use such kinds of fact tables

Asked by: Interview Candidate | Asked on: Jun 29th, 2005
Showing Answers 1 - 5 of 5 Answers
Santanu Patra

Answered On : Jun 29th, 2005

Semi-Additive: Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others. For example: 
Current_Balance and Profit_Margin are the facts. Current_Balance is a semi-additive fact, as it makes sense to add them up for all accounts (what's the total current balance for all accounts in the bank?), but it does not make sense to add them up through time (adding up all current balances for a given account for each day of the month does not give us any useful information

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Santanu Patra

Answered On : Jun 29th, 2005

A factless fact table captures the many-to-many relationships between 
dimensions, but contains no numeric or textual facts. They are often used to record events or 
coverage information. Common examples of factless fact tables include: 
- Identifying product promotion events (to determine promoted products that didnt sell) 
- Tracking student attendance or registration events 
- Tracking insurance-related accident events 
- Identifying building, facility, and equipment schedules for a hospital or university

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Answered On : Jul 25th, 2007

There has been so much talk about numeric additive values in fact tables that it may come as a surprise that two kinds of very useful fact tables don't have any facts at all! They may consist of nothing but keys. These are called factless fact tables.

first type of factless fact table is a table that records an event. Many event-tracking tables in dimensional data warehouses turn out to be factless.

A second kind of factless fact table is called a coverage table. Coverage tables are frequently needed when a primary fact table in a dimensional data warehouse is sparse.

Good Luck

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Answered On : Aug 3rd, 2007

Semi-additive facts are those facts which can be aggregate according to the context. so, it can contain a fact but the factless fact table does not contain fact's but it contains the dimmentions. It's a type of a dimmentions.

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Answered On : Feb 11th, 2010

View all answers by divya29july

Factless Fact table:

Consider an example of Product on promotion, the fact table will contain information of only the products that were on sale and sold but not of those that did not sell as the fact table is not meant to keep null values, thus we refer these tables as factless fact table as it does not have measurement metrics.

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