Describe three types of slowly changing dimension (SCDs) and discuss the best SCD Type to track changes over time to a member’s home address.
What will be an ideal response?
Most common techniques for dealing with SCDs that are not significant are called Type 1 and those
that are significant are called Types 2 and 3.
A Type 1 SCD overwrites the existing attribute value with the new value. This gives no tracking record
of historical values.
A Type 2 SCD captures the attribute values that were in effect at a point in time and relates them to the
business events in which they participated.
When a change occurs to a Type 2 SCD, a new record is created in the dimension table to capture the
new values that are to take effect from that point onwards or to the next change.
Type 3 SCD creates separate attributes for both the old and new attribute values. However, Type 3 is
less common because it involves changing physical tables and is not very scalable.
Only Type 2 or 3 should be discuss for the member’s home address SCD as Type 1 does not track
changes.
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