Query Subjects That Represent a Level of Hierarchy
One frequent case of an ambiguously defined query subject that is not harmful is where the query subject represents an intermediate level of a descriptive hierarchy. One example is the following Product hierarchy.
In this example, both Product type and Product could be identified as being ambiguously defined. However, this ambiguity is not detrimental to either the results generated or the performance of any query using one or more of these query subjects. You do not need to fix this query pattern because, using the rules for fact detection, only one fact is identified in any query that combines an item from the Product forecast or Sales query subjects. It remains a best practice to collapse hierarchies into a single regular dimension when modeling for analysis purposes.
Some queries that can be written using this example include the following:
| Items from these query subjects are used in a query: | Query subject that behaves as a fact in the query: |
|---|---|
| Product line and Product type | Product type |
| Product line, Product type, and Product | Product |
| Product line, Product type, Product, and Sales | Sales |
| Product line and Sales | Sales |
| Product type and Product forecast | Product forecast |