A library database records the authors and the publisher of each book. Normalize the following relation and indicate the primary and foreign key attribute types:

R (ISBN, title, author(name, date_of_birth), publisher(name, address(streetnr, streetname, zipcode, city)), pages, price)

The assumptions are:

each book has a unique ISBN number;

each author has a unique name;

each publisher has a unique name;

a book can have multiple authors;

an author can write more than one book;

a publisher can publish more than one book;

a book has only one publisher;

a publisher has only one address.

Suppose that one book can have multiple publishers. How can you extend your model to accommodate this? Where would you put the attribute type number_of_copies?