Slowly Changing Dimension

Slowly Changing Dimension

Dimension is a term in data management and data warehousing. It's the logical groupings of data such as geographical location, customer or product information. With Slowly Changing Dimensions (SCDs) data changes slowly, rather than changing on a time-based, regular schedule.

For example, you may have a dimension in your database that tracks the sales records of your company's salespeople. Creating sales reports seems simple enough, until a salesperson is transferred from one regional office to another. How do you record such a change in your sales dimension?

You could calculate the sum or average of each salespersons sales, but if you use that to compare the performance of salesmen, that might give misleading information. If the salesperson was transferred and used to work in a hot market where sales were easy, and now works in a market where sales are infrequent, his/her totals will look much stronger than the other salespeople in their new region. Or you could create a second salesperson record and treat the transferred person as a new sales person, but that creates problems.

Dealing with these issues involves SCD management methodologies referred to as Type 0 through 6. Type 6 SCDs are also sometimes called Hybrid SCDs.