Library Database (cont’d)

• Step 4. Determine level of participation

  • Since each book does not have to be authored (anonymous) and since each author does not have to write a book (may make CD) the level of participation is optional for both sides of the relationship of AUTHOR-writes-BOOK combination

N

1

N

• For the PUBLISHER-publishes-BOOK combination, the level of participation for PUBLISHER is optional (publishers do not necessarily have to publish a book, perhaps newsletters) and the level of participation for the BOOK side is mandatory (each book must have a publisher)

(0, N)

(1,1)

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