Saturday, May 16, 2015

What is a Junk Dimension?

Dimension represents entities that will be used for analyzing facts in the data warehouse. There are different type of dimensions like Regular, Slowly Changing, Self-Referencing and Junk. Many know about all of these except Junk.

Junk dimension is a dimension that combines multiple dimensions that have attributes with low cardinality and only few discrete values. This makes the process clean and reduce the complexity of the dimensional model.

Here is an example. Assume that three dimensions have been identified during requirement gathering process and they hold small number of values;

Rather than maintaining three tables for these three dimension, one dimension table can be introduced combining all values;

It represents all possible combinations of three dimensions and can be used with Fact tables without any issue. This dimension is called as Junk Dimension.

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