The need for Detailed Information
This is the area of the data warehouse that stores all the detailed information in the starflake schema. In many cases, all the detailed information is not held online the whole time, but aggregated to the next level of detail, and the detailed information is then offloaded into tape archive. On a rolling basis, detailed information is loaded into the warehouse to supplement the aggregated data.
For example, it is very common to store transactions at the level of product by store by day for retail sales analysis data warehouses. This information is perfectly appropriate for analyzing actual sales against projected sales. What this degree of detail does not provide is basket analysis: that is, because all transactions for a particular product in a particular store are aggregated to the whole of the day, it is not possible to examine a specific customer basket transaction, or analyze components within the basket.
In order to determine what degree of detail is required, ask yourself the question - What activities within the business process require detailed, individual transactions? This should indicate what user requirements exist to store base transactions. If the business requirement for detailed information is weak or very specific, it may be possible to satisfy it by storing a rolling three-month detailed history. This could satisfy the need to have some detailed information, without too much impact on the storage requirements. This style of operation is assisted if all historical changes to dimension data are stored online - that is, dimension tables.