# Problem Deciding Facts in an OLAP

• ### Question

• Hi Folks , I just started reading about OLAP and I had a couple of questions in mind.. so please bare with me ....

Now In short I know there are two databases one is my transactional database (OLTP) and one is my (Analytical Database OLAP) anyways While desiging my OLDAP i ran into a couple of problems deciding dimensions and facts.. Luckily i ran into a small consisive article at  http://nexus.realtimepublishers.com/tips/Data_Warehousing/Why_Is_OLAP_Faster_Than_OLTP.php which explained the concept of dimensions pretty well . It defined the dimesnions as

"Dimensions are the categories of data analysis. The rule of thumb is: When a report is requested "by" something, that something is usually a dimension. For example, in a revenue report by month by sales region, the two dimensions needed are time and sales region. For this reason, OLAP analysts often nickname dimensions the "bys." Typical dimensions include product, time, and region."

Question:

Sorry for making you guys read all that but i thought it would be best to show all my cards b4 i went ahead and asked a question.

Anyways I am having trouble deciding the facts ?? I still dont know what columns are suppose to be in my facts table ?? I know that to be placed as a column in the fact table , Each dimension column has a foreign-key relationship to the related dimension table..... I hope I got that through....

Any Example would be appreciated which helps in deciding what columns are supposed to be in my "Facts Table" ??? thanks..

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Friday, November 12, 2010 9:59 PM

### All replies

• Wikipedia states that " Measures are derived from the records in the fact table and dimensions are derived from the dimensions Table."

I read from the previous link which i mentioned the definition of Measures:

"Measures are the key performance indicators that you want to evaluate. To determine which of the numbers in the data might be measures, a rule of thumb is: If a number makes sense when it is aggregated, then it is a measure. For example, it makes sense to aggregate daily volume to month, quarter and year. On the other hand, aggregating zip codes or telephone numbers would not make sense; therefore, zip codes and telephone numbers are not measures. Typical measures include volume, sales, and cost."

so is it correct that all the measures in a DB end up in the fact table ??

A candle loses nothing by lighting another candle.
Friday, November 12, 2010 10:55 PM