oracle DB design question

hello,
If I have an entity (for instance a "book") which is ALWAYS related to another entity (for instance an "author"). I have one decoding table for "authors" (numeric sequential code + description). Which way is preferred when designing the "books" table: 1. *author_code *book_code au_name ... (2 primary keys) 2. *book_code bk_name author_code ... (1 primary key and FK+index on author_code)
I am asking because suppose there is a third table containing information on the entity "reader" whereas each reader likes to read books by a specific author. readers table would look like this:
(*reader_code reader_name author_code(FK) age....)
If i have a table containg the books each reader has read, where i want to verify through it, the book is by the author he likes. Should this table have: 1. three PK for solution (1) thus verifying integrity with a FK.
(*author_code *book_code *reader_code)

2. two PK for solution (2) thus verifying integrity with say a trigger
(*reader_code *book_code)

Thanks for any help

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