An item that is in the fact table but is stripped off of its description, because the description belongs in dimension table, is referred to as Degenerated Dimension. Since it looks like dimension, but is really in fact table and has been degenerated of its description, hence is called degenerated dimension.
Another definition of Degenerated Dimension: A fact or “degenerate” dimension has a one-to-one relationship with the facts, such as a transaction number. The degenerate dimension is not used for analysis as such, but rather for identification. For example, to locate a specific transaction or to identify the transactions that make up an aggregate cell.
Now coming to the slowly changing dimensions (SCD) and Slowly Growing Dimensions (SGD): I would like to classify them to be more of an attributes of dimensions its self. Although other might disagree to this view but Slowly Changing Dimensions are basically those dimensions whose key value will remain static but description might change over the period of time.
For example, the product id in a companies, product line might remain the same, but the description might change from time to time, hence, product dimension is called slowly changing dimension. Lets consider a customer dimension, which will have a unique customer id but the customer name (company name) might change periodically due to buy out / acquisitions, Hence, slowly changing dimension, as customer number is static but customer name is changing, However, on the other hand the company will add more customers to its existing list of customers and it is highly unlikely that the company will acquire astronomical number of customer over night (wouldn’t the company CEO love that) hence, the customer dimension is both a Slowly changing as well as slowly growing dimension.
What is a JUNK Dimension?
