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The correct data model for a many-to-many relationship is shown in Figure 4-33.
FIguRE 4-33 The correct way to build the many-to-many data model.
When present, many-to-many relationships violate the rule of the star schema that imposes
one as the maximum depth of the chain of relationships between fact tables and dimensions.
Nevertheless, you do not absolutely need to conform to that rule. The rule helps you create
data models that are easy to understand, but if you need more power to express complex
relationships such as many to many, you can safely violate the rule.
Many-to-many relationships are not natively supported in PowerPivot. Later on, in Chapter 10,
“PowerPivot Data Model Patterns,” you learn how to master many-to-many relationships to
make them solve some of the most common patterns of data models.