Business Intelligence Dictionary: Facts And Dimensions Explained | NSBI
Facts | Definition
NSBI Dictionary defines Facts as numeric Measures of a business process.
Dimensions | Definition
NSBI Dictionary defines Dimensions as Attributes used to describe measures and slice them from different perspectives.
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Facts and Dimensions | Example
"SalesRevenue" is a typical fact used to describe the revenue from a sale.
This single sale, however, may be sliced from a different angle according to the business needs., e.g. "Employee" that made the sale, "Time" when the sale was recorded, "Location" where it happened, etc. All these are attributes, that describe the fact - Dimensions.
Dimensions | Classification
There is a special kind of Dimensions, called Conformed Dimensions. NSBI Dictionary defines Conformed dimensions as dimensions that have consistent meaning in all fact tables and all source databases. A typical example for a conformed dimension is "Time". Usually time has the same meaning everywhere.
Note: In some more complicated scenarios this may not be the case. Consider days of the week. In North America you may see Sunday as the first day of the week, while Europe considers Monday as Day 1. These cases must be handled separately.
Slowly Changing Dimensions
Slowly changing dimensions is a term introduced by Kimball Group and aims to describe dimensions that are expected to change over time. The Data Warehouse will have to handle such occasions. We will have a separate article that goes into details - click here.
Facts Classification - Additive Measures
Facts may also be further classified considering their "Additiveness" factor. Facts may be:
- Additive - measures that can be added across all dimensions (e.g. SalesRevenue)
- Non-Additive - measure which addition won't make any business sales (e.g. adding profit % margins)
- Semi Additive - measured that can be added across some dimensions (e.g. Balance Sheet Capital is consolidated monthly - it is additive across different organizations, but non-additive by time since the sum of two consecutive months won't give any reasonable result for month 3).