How to design the cube

Hi Experts,

Sales data (by Product) is available from the source system. However the analytical reporting is done Brand wise. The association of Product and Brand changes every year. The reports should show the association as on the transaction date. Which is the best way to model the Product-Brand combination?

1. Product as a dimension member, Brand as a time independent navigational attribute of Product
2. Brand as a dimension member, Product as a time independent navigational attribute of Brand
3. Both Product and Brand as dimension members
4. External hierarchy created on Product with brand as external characteristic.

Please let me know the logic

Thanks

Venkat