A specific computer mouse might be in the Product Category
Hardware, the Product Subcategory Peripherals, the Product Group Mice, with the
individual product existing at the SKU level. There are also other columns that more
fully describe the product and might include information such as color, price, weight,
height, width, product code, and more.
Time Dimension
Year
Location Dimension
Country
Quarter State/Province
Month City
Day Plant
Assembly Line
Figure 3-2 Simple dimensions and their hierarchies
36 B u s i n e s s I n t e l l i g e n c e w i t h M i c r o s o f t O f f i c e P e r f o r m a n c e P o i n t S e r v e r 2 0 0 7
The values for such items as the Product Category and Product Subcategory are
stored as text in the dimension table. This is the part of a dimension table that is
denormalized; the data is repeated many times instead of minimizing storage using
relational techniques. This may seem wasteful, but as will be shown later, the storage
used by dimension tables is minor in the overall scheme of the warehouse.
Due to restrictions on page size, the columns of a single record are broken
into multiple pieces. Table 3-1 shows several records as they would appear in the
dimension table.
Note that in some cases, architects do normalize dimension tables somewhat. In
this case, one separate table might be made for Product Category and another for
Product Subcategory. This design is called a snowflake schema and is sometimes
seen in large warehouses.
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