The Location dimension
has Country, State/Province, City, Plant, and Assembly Line levels. Actual data
can exist at each level; for example, the data may include years 2006, 2007, and
2008. Each one of these is a member. Therefore, 2007 is a member at the year level.
The easy way to think of this is that any actual data value is a member. Where it is
located in the hierarchy is its level.
A single dimension can actually contain multiple hierarchies. One common
example is a Time dimension, which may contain one hierarchy for a fiscal calendar
and a different hierarchy for a Julian calendar. The hierarchies might have the same
levels, but simply a different start date; the company might start its fiscal year on
July 1, for example. On the other hand, the hierarchies might contain different levels.
The fiscal hierarchy might contain Year, Quarter, Week, and Day, while the Julian
calendar might contain Year, Quarter, Month, and Day. There is nothing wrong with
either of these hierarchies; each one is simply a different way of analyzing the data.
The Structure of a Dimension Table
A dimension table is highly denormalized, which means it contains repeated data and
full text descriptions, rather than key values which join to other tables. A dimension
table contains columns which fully describe the item, and each row represents a
unique item. For example, an individual product exists in a product hierarchy. The
hierarchy consists of the levels Product Category, Product Subcategory, Product
Group, and SKU.
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