The context of the business process may change over time. Slowly Changing Dimension is the technique to manage the change history of dimension table which the context changes slowly.
There are many ways to manage changing dimension. See below definition quoted from internet resource. We usually use type 0, 1 and 2 in slow changing dimensions while type 4 is useful in Rapidly Changing dimension.
Type 0: Retain original
Type 1: Overwrite
Type 2: Add new row
Type 3: Add new attribute
Type 4: Add mini-dimension
Type 5: Add mini-dimension and Type 1 outrigger
Type 6: Add Type 1 attributes to Type 2 dimension
Type 7: Dual Type 1 and Type 2 dimensions
Type 0 simply ignores any change and keep the original context. Type 1, in other way, overwrites the context values by the latest change. These two implementations are simple that won't keep series of change history but only one version. Type 2 is the implementation that keeps changing history. We usually maintain the change history with effective dates columns. They are the most common way to manage slowly changing dimension.
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