An interesting challenge arises when changes are being made to the EDW. If the current requirements are to remove some data that is no longer valid. For example a product or service is being removed and so data which was being extracted is no longer available to be extracted. The question is do we remove the historic data from EDW or simply remove the data structure from the updating process and keep the historic data. The current structure has now different form the old data structure.
I think to maintain the integrity of the EDW, the old data should be preserved. However if maintaining the out of date data cost more, who should pay. An interesting architectural and philosophical issue.