RETAIL BOOK SHOP FACT and AUTHOR dims

Modelling a Book shop chain -

Dimensions -

1) Book ( Will have vendor details as attributes )
2) Time
3) Store
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A book can have mutliple authors and an author can write multiple books.
I don't think FACT should have author related keys but still..

there are 2 ways..

a) Author dim is snow flaked from Book dimension. Book and Author connected on natural keys with 1-n relationship.

b) Create bridge between FACT and AUTHOR dim.