Question:
(a) Can a set of data requirements be correctly modelled by two or more different ER diagrams? Explain your answer. You may use a small example, if you think it will help your explanation.
(b) What is a recursive relationship? Give an example of a many to many recursive relationship.
This question refers to the Appendix where the relational schema for an online DVD rental system is defined.
(c) Express the following queries using relational algebra:
(i) Find all DVD titles with their certificate being ‘15' and their type name being ‘Drama'
(ii) Find names of all members and the titles of DVDs, which they have rented between 1st
May 2007 and 31st
May 2007
(iii) Find names of all the members who have rented any DVD with type name ‘Comedy' but not any DVD with Type name ‘Action'