Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Data Warehouse Design

HIERARCHICAL ATTRIBUTE DESIGN

Hierarchies are especially difficult to maintain in a data warehouse. Unlike finite attributes, hierarchical classifications may assign many values when an item is added to an Oracle data warehouse. The hierarchical classification displayed in Figure 4.14 shows a hierarchical attribute classification for a product.

Figure 4.14 A classification hierarchy for a product.

For example, when a transaction for the purchase of chicken wings is recorded, attributes made for the transaction need to include the sale of a chicken product, a meat product, and a food product. As such, a mechanism needs to be devised to store the hierarchy of attributes in a meaningful way and to insert the proper values each time a row is added to the fact table.
In our example, we have the following two methods for representing our hierarchy of product attributes:

1. Assign an arbitrary level classification for each level in the hierarchy. Because each level is mutually exclusive (i.e., the product cannot be both food and nonfood), the following scheme would be the most efficient use of storage in the fact table:

level_one char(1)
CONSTRAINT level_one_check
CHECK (level_one in (‘F’,‘N’);
level_two char(1)
CONSTRAINT level_two_check
CHECK (level_two in (‘A’,‘V’,’P’,’T’);
level_three char(1)
CONSTRAINT level_three_check
CHECK (level_three in (‘U’,‘B’,‘C’);

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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:
http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm