I created a database to remind me who lends me a book and which is this book among all books I have in my library. So in this database I recorded several books with their title, author, and year of their publication. When I select a book, it is indicated who lent it to me. It is very useful when you are a big reader because sometimes you end up with a huge stacks of books and you don't remember which book is whose. At this end I created two entities; one for "Book" and another one for "Friend". A friend could lend to me one or several books while a book can be lent by one and only one friend.