In many cases this is a perfectly adequate strategy. For querying and reporting, this purged data and the current data may be stored in the data warehouse where there presumably is less of a need to control expected response time or the expected response time is at a much higher level. For example, if you want a report of the salaries of employees at grade Level 3 as of the beginning of each month in 1997, you may not be able to do this because you only have a record of current employee grade level. The concern here is security. For example, data warehousing may be interesting to firms that want to allow report and querying only over the Internet.
Some firms implement data warehousing for all the reasons cited.
Some firm implement data warehousing for only one of the reasons cited. If you examine the list you may be struck that need for data warehousing is mainly caused by the limitations of transaction processing systems. These limitations of transaction processing systems are not, however, inherent. That is, the limitations will not be in every implementation of a transaction processing system. Also, the limitations of transaction processing systems will vary in how crippling they are.