When you define a new cube dimension or a new measure group, Analysis Services will try to detect if a fact dimension relationship exists and then set the dimension usage setting to Fact. You can view or edit a fact dimension relationship on the Dimension Usage tab of Cube Designer. The fact relationship between a dimension and a measure group has the following constraints:
A cube dimension can have only one fact relationship to a particular measure group.
A cube dimension can have separate fact relationships to multiple measure groups.
The granularity attribute for the relationship must be the key attribute (such as Transaction Number) for the dimension. This creates a one-to-one relationship between the dimension and facts in the fact table.