Data Modeling: Degenerate Dimension

A degenerate dimension (DD) acts, as a dimension key in the fact table, dose not have a corresponding dimension table because all its interesting attributes have already been placed in other analytic dimensions. Even though there is no corresponding dimension table of attributes, degenerate dimensions can be quite useful for grouping together related fact table’s rows.

Degenerate dimensions are useful as they tie the transactions, or events, in the fact table back to real-life items - invoices, orders and so on - and they can be a quick way to group together similar transactions for further analysis.

Degenerate dimensions also reduce the need for lookup tables in the ETL processes since there is not actual dimension table associate with a degenerate dimension.

Some examples for degenerate dimensions are, order id, invoice id of a sales order, a flag, which used to indicate if an order is invoiced or not invoiced.

In general, the decision to use degenerate dimensions is often based on the desire to provide a direct reference back to a transactional system without the overhead of maintaining a separate dimension table.


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