It??™s also more complex than this, because
a single table can act as both a fact and dimension table, but that is a discussion
beyond the scope of this book.
After choosing the facts and dimensions, it is often necessary to map a Time
dimension. Time or Date dimensions exist in almost every cube. There are certain
functions built into Analysis Services that only work when a dimension has been
identified as a Time dimension. These functions are useful for performing actions
such as period over period growth calculations, moving averages, and so forth. The
ability to map a Time dimension to expected time values is flexible and includes
both calendar and fiscal categories.
The wizard next tries to determine the measures that exist in the fact tables.
Normally the wizard does a decent job identifying the measures by looking in the
fact tables for numeric columns. Sometimes it includes some of the foreign keys
56 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
as measures because they are numeric fields, but key values are normally just
automatically incrementing values, so making them measures doesn??™t make sense.
Fortunately, any fields chosen as measures that shouldn??™t be there are easy enough
to remove before continuing. The wizard also automatically adds a count to the
measures for each fact table.
By default, each fact table has its measures placed into its own Measure Group.
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