I'm a newbie to data warehousing and I've been reading articles and watching videos on the principles but I'm a bit confused as to how I would take the design below and convert it into a star schema.
in this example i assume that the fact table is (order-orderitem-book)
And the measures is (category-customer-time)
My question is about book author how can we put is as measure? Is it allowed to put many to many relationship in star schema ?? 
And if i am wrong how to draw star schema to this relatonal db?
![enter image description here](https://i.stack.imgur.com/THqjr.jpg)