MITS4003 Database Systems
Take-Home Exercise – 2 of Lesson – 2
June 2018 Task 1: E-R Diagram
MITS4003 Exercise 2
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2.1 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. Each insurance policy covers one or more cars and has one or more premium payments associated with it. Each payment is for a particular period of time and has an associated due date, and the date when the payment was received. What is a model?
2.2 Consider a database used to record the marks that students get in different exams of different course offerings (sections).
a. Construct an E-R diagram that models exams as entities, and uses a ternary relationship, for the database.
b. Construct an alternative E-R diagram that uses only a binary relationship between student and section. Make sure that only one relationship exists between a particular student and section pair, yet you can represent the marks that a student gets in different exams.
Task 2: Problems 2.3 A weak entity set can always be made into a strong entity set by adding to its attributes the primary- key attributes of its identifying entity set. Outline what sort of redundancy will result if we do so.
2.4 An E-R diagram can be viewed as a graph. What do the following mean in terms of the structure of an enterprise schema?
a. The graph is disconnected.
b. The graph has a cycle.
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