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Data Transformation Analysis
Oracle Tips by Burleson Consulting
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The Data Warehouse Development Life Cycle
DATA TRANSFORMATION ANALYSIS
Also recall that Guttbaum’s has a fact table in which each item
appears as a separate row in the table. In this way, correlational
analysis can be used to determine associations between grocery
items. However, even though the database stores a row for each item
in a transaction, there is no direct information about the different
categories in which each item participates. A transaction may record
the sale of two pounds of calf livers, but it does not record the
fact that calf liver is a part of the beef category, that beef is a
part of the meat category, and that meat is a part of the food
category. Guttbaum’s classification hierarchy might look something
like the hierarchy shown in Figure 3.18.
Figure 3.18 A classification hierarchy for Guttbaum’s Grocery.
In practice, just about every “object” in a data warehouse could
become a part of a classification hierarchy, and because a data
warehouse is subject-oriented, it is usually the subject that is
classified. Another example would be a data warehouse for a
bookstore where sales of books would need to be classified into
fiction, non-fiction, and so on. The identification of these
classification hierarchies is critical to warehouse analysis because
a method must be designed to allow the subjects to be categorized
for queries.
As noted earlier, the idea of classification hierarchies in a data
warehouse analysis has parallels in the object-oriented world. In a
C++ program, class hierarchies can be created to distinguish between
different “types” of an object, where each type has its own data
items and behaviors. The same principle applies to the data
warehouse. The end user may want to query, How many paper products
were sold last week? Unless our warehouse knows which items
participate in the paper products categories, the warehouse will not
be able to easily answer this query.
As we will discuss in the next chapter, classification hierarchies
are added to basic entity/relation models so that the data warehouse
analyst can describe each type of item. In Figure 3.19, you can see
that a bill-of-material’s entity for an item has been extended to
allow for different types of items. We’ll take a closer look at
extending entity/relation models in the next chapter, when we begin
to apply physical techniques to our logical systems analysis.
Figure 3.19 An extension of an entity/relation model.
This is an excerpt from "High Performance
Data Warehousing".
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