# Entity-relationship Model and E-r Diagram

**Topics:**Entity-relationship model, Entity, Unified Modeling Language

**Pages:**2 (400 words)

**Published:**April 28, 2013

1. (Exercise 2.1) Explain the distinctions among the terms primary key, candidate key, and superkey. 2. (Exercise 2.2) Construct an E-R diagram for a car-insurance company whose customers own one or more cars each. Each car has associated with it zero to any number of recorded accidents. 3. (Exercise 2.4) A university registrar’s office maintains data about the following entities: (a) courses, including number, title, credits, syllabus, and prerequisites; (b) course offerings, including course number, year, semester, section number, instructor(s), timings, and classroom; (c) students, including student-id, name, and program; and (d) instructors, including identification number, name, department, and title. Further, the enrollment of students in courses and grades awarded to students in each course they are enrolled for must be appropriately modeled. Construct an E-R diagram for the registrar’s office. Document all assumptions that you make about the mapping constraints. 4. (Exercise 2.5) Consider a database used to record the marks that students get in different exams of different course offerings. a. b. Construct an E-R diagram that models exams as entities, and uses a ternary relationship, for the above database. Construct an alternative E-R diagram that uses only a binary relationship between students and course-offerings. Make sure that only one relationship exists between a particular student and course-offering pair, yet you can represent the marks that a student gets in different exams of a course offering.

5. (Exercise 2.12) Consider the E-R diagram in Figure 2.29, which models an online bookstore. a. b. List the entity sets and their primary keys. Suppose the...

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