The 4tuples in a 4ary relation represent these attributes of

The 4-tuples in a 4-ary relation represent these attributes of published books: title, ISBN, publication date, number of pages. a) What is a likely primary key for this relation? b) Under what conditions would (title,publicationdate) be a composite key? c) Under what conditions would (title, number of pages) be a composite key?

Solution

a) ISBN is unique for each book, thus it is likely the one and only primary key for the relation.

b) (title,publicationdate) could be a composite key, as long as there were not two books with same title published on the same date (or year, publication date of a book is usuallly given as year).

c) (title, number of pages) could be a composite key as long as no two books are having same title and same number of pages. This will never be the case, thus this composite key is less likely possible.