Specify relational algebra expression for the following descriptions on the Library database schema shown in Figure 4.6

a.) Retrieve the names of customer who borrow book from all the branches.

b.) Retrieve the names of authors whose books have never been borrowed.

BOOK Book id Title Publisher name BOOK AUTHORS Book id Author_name PUBLISHER Name Address Phone BOOK COPIES Book id Branch id No of copies BOOK LOANS Book id Branch id Card no Date out Due date LIBRARY BRANCH Branch id Branch_name Address BORROWER Figure 4.6 Card no Name Address Phone relational database schema for a LIBRARY database