For many dimensions, we are not usually worried about changes being made in the underlying system. If a salesperson gets married and their surname changes from "Smith" to "Jones," we just reload the QlikView document and the new surname will appear in the selectors. However, if the same person changes from the inside sales team to the northwest sales team, just updating the data means that sales attributed to that salesperson will no longer get attributed to the correct team.
These changes to the dimensions do not happen very frequently and are called slowly changing dimensions (SCDs). Kimball defines eight different methods of handling SCDs, from Type 0 to Type 7. The first example discussed previously, the change of surname, is an example of Type 1—simply update the value (Type 0 says to use the original value). The second change, where the sales team is updated, should be handled by Type 2—add a new row to the dimension table. Type 1 and Type 2 will...