2.4. Sources of Data
Returning to the example of the report from Table 2.1, it is vital to understand how the fact table (i.e., Table 2.2) and other tables were filled in with data. For instance, in order to calculate the sales quantity for a given product, one must
- check which transactional data system the source data (i.e., the invoices or orders, on the basis of which one can specify the quantity of sales) are stored in.
- determine the interface between the system with the source data and the data warehouse and enter suitable data. Information from the given day should be added to the previous data to extend the history of sales by another day.
- aggregate the data from the invoices, which are single transactional business events, to show the ...