SCD

Slowly Changing Dimension

Pattern for tracking changes to dimensional data over time.

When you'd see it: Data-warehouse modeling. SCD patterns decide how to handle attributes that change over time, like a customer's address.

Why it matters: SCD is the set of patterns for tracking how dimensional data changes, such as keeping history versus overwriting. Choosing the wrong type silently loses the history a report later needs.

Common mistakes: Overwriting changing attributes (Type 1) when the business needs history (Type 2). Once overwritten, the past is gone and cannot be reconstructed.