Exercise 1: ER-Diagrams Due: November 5, Ross closing time

Transcription

1 Exercise 1: E-Diagrams Due: November 5, oss closing time Name: Login: Student Number: Print out this exercise and answer the questions on the printout. emember to register for the course so that your exercise may be graded. Problem 1 (0 Points) egister for the database course using the url Problem 2 (35 points) Below we present several entity relationship diagrams for modeling information about authors, editors and books. Note that is the key of, is the key of and is the key of. For each of the entity relationship diagrams below: (a) State briefly the meaning of the diagram. Emphasize the constraints in the diagrams. (b) Suppose that there are 300 authors, 1000 books and 10 editors. What is the maximal number of triples that contains? (c) Suppose that there are 300 authors, 1000 books and 10 editors. What is the minimal number of triples that contains? (1a) Meaning: (1b) Maximal number of triples: (1c) Minimal number of triples: 1

2 (2a) Meaning: (2b) Maximal number of triples: (2c) Minimal number of triples: (3a) Meaning: (3b) Maximal number of triples: (3c) Minimal number of triples: (4a) Meaning: (4b) Maximal number of triples: (4c) Minimal number of triples: 2

3 (5a) Meaning: (5b) Maximal number of triples: (5c) Minimal number of triples: Problem 3 (25 Points) 1. As in Problem 2, we consider information about, and. We wish to store information about which author wrote which book with which editor. Two basic approaches can be taken to model this information: Edits Contact Writes (a) (b) (a) Assuming that there are no further constraints on the information, which of the two diagrams presented are more suitable for modeling the information? Can the information be captured in both diagrams? Explain. 3

4 (b) Suppose that each book is edited by at most one editor. Can you add edge constraints (arrows) to the diagram on the left in order to capture this information? What about the diagram on right? Explain. 2. What is wrong with using the following diagram to model the information? Writes Problem 4 (40 Points) Congratulations! You have gotten a job planning databases for the European Union. Your first on job assignment is to help the various countries maintain information about their inhabitants. Your model should capture the following information: In each country, there are provinces, which contain towns. There cannot be two provinces with the same name in a single country. Similarly, there cannot be two towns with the same name in a single province. People live in towns. Men and women work in a town. Children learn in a school in a town. A person can be a man, a woman, or a child, and has a first-name, last-name, id, and birthday. Children are any people under the age of 18. 4

5 A man can be married to a woman (polygamy is not allowed, i.e., one man can be married only to one woman). Although the Pope strongly disapproves, divorce, and subsequent remarriage, is possible. For each marriage, store the date of the marriage and information about who are the children of the married couple. You should assume that the parents of a child were married at the time of his birth. Draw an entity relationship diagram to model the information described above. emember to put edge constraints (arrows) and participation constraints (thick lines) where needed. Underline the key attributes of each entity in the diagram. If you use the ISA relationship, state any covering and overlap constraints that hold. Make any necessary and logical assumptions. State any such assumptions clearly. If there are any constraints in the problem that could not be expressed in the diagram, state these clearly. 5