Defining a Many-to-Many Relationship and Many-to-Many Relationship Properties
The many-to-many dimension relationship defines an association between a dimension and a measure group by specifying an intermediate fact table that is joined to the dimension table. An intermediate dimension table is in turn joined to both the intermediate fact table and to the fact table on which the measure group specified by the relationship is based. The many-to-many relationships between the intermediate fact table and both the dimension table in the relationship and the intermediate dimension create the many-to-many relationships between members of the primary dimension and the measures in the measure group specified by the relationship.
Many-to-many dimensions expand the dimensional model beyond the classic star schema, and support complex analytics when dimensions are not directly related to a fact table.