Star schema, which maintains one-to-many relationships between dimensions and a fact table is widely accepted as the most viable data representation for dimensional analysis.
Realworld DW schema, however, frequently includes many-to-many relationships between a dimensionand a fact table.
Issues of many-to-many relationships.
1. losing the simplicity of the star schema structure
2. increasing complexity in forming queries, and
3. degrading query performance by adding more joins.
Two ad-hoc methods to resolve
1. Denormalizing the dimension tables.
2. Building the Bridge Table.
To find more information : go to the white paper An Analysis of Many-to-Many Relationships Between Fact andDimension Tables in Dimensional Modeling
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