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by Burleson Consulting

The Data Warehouse Development Life Cycle

The Role Of Functional Decomposition
The principles of top-down analysis tells us to begin our data flow diagram (DFD) at a very general level. The entire system is viewed as a single process, and this view is called a Context Level DFD. Next, the DFD is decomposed, and levels of detail are added to the model. Any process that can be identified can probably be subdivided to smaller processes, and it is possible to decompose a DFD to the level where each process represents a single statement. An extreme example of functional decomposition would be showing a statement such as add 1 to counter as a separate process on the data flow diagram. The pivotal question is: At what point should the developer stop decomposing the processes?

Theoreticians such as Gane and Sarson tell us that a DFD should be decomposed to the functional primitive level, where each process bubble performs one granular function. Under this definition, one could consider that the place_an_order behavior performs only one function and is therefore a functional primitive process. A good rule of thumb for data warehouse analysis, especially when the warehouse is intended to be used with a relational database, is that a DFD should be decomposed to the level where each process corresponds to an SQL operation. This allows the use of triggers within a relational database and greatly simplifies the data warehouse design.

As you are probably beginning to see, the level of partitioning is critical for a successful data warehouse systems analysis. Let’s explore this concept of partitioning a little further. In a traditional systems analysis, the place_order behavior is sufficiently partitioned, whereby the place_order process would become a single computer program. This program would perform all of the data manipulation and would have many DML verbs embedded within the code (see Figure 3.4). Following is what the mini-spec might look like for a place_order process:

This is an excerpt from "High Performance Data Warehousing". To learn more about Oracle, try "Oracle Tuning: The Definitive Reference", by Donald K. Burleson.  You can buy it direct from the publisher at 30% off here:


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