Data from diverse operational applications is integrated

Data inconsistencies are removed; data from diverse operational applications is integrated. 

Figure 2-2 The data warehouse is integrated:

Here are some of the items that would need standardization:

• Naming conventions
• Codes
• Data attributes
• Measurements

Time-Variant Data

For an operational system the stored data contains the current values, In an accounts receivable system, the balance k the current outstanding balance in the customer's account. In an order entry system, the status of an order is the cm rent status of the order. In a con-St1111C1 loans application, the balance amount owed by the customer is the current amount. Of course, we store some past transactions in operational systems, but, essentially, operational systems reflect current information because these systems support day-to-day current operations.

On the other hands, the data in the data warehouse is meant for analysis and decision making. If a user is looking at the buying pattern of a specific customer, the user needs data not only about the current purchase, but on the past purchases as well. When a user wants to find out the reason for the drop in sales in the North East division, the user needs all the sales data-for that division over a period extending back in time. When an analyst in a grocery chain wants to promote two or more products together, that analyst wants sales' of the selected products over a number of past quarters.

A data warehouse, because of the very nature of its purpose, has to contain historical data, not just current values. Data is stored as snapshots over past and current periods. Every data structure in the data Warehouse contains the time element. You will find historical snapshots of the operational data in the data warehouse. This aspect of the data ware-house is quite significant for both the design and the implementation phases.

For example, in a data warehouse containing units of sale, the quantity stored in each file record or table row relates to a specific tune element. Depending on the level of the details in the data warehouse, the sales quantity in a record may relate to a specific date, week month, or quarter.

The time-variant nature ot the data in a data warehouse:

• Allows for analysis of the past
• Relates information to the present
• Enables forecasts for Mc future