December
1998 QUESTION 4 Total Marks: 20 Marks |
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| (a) | In the Entity-Relationshop (E-R) model, what is
meant by an existence dependency? What is the name for an entity-type that has an
existence dependency?
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[2] |
| (b) | Draw an E-R diagram for each of the following situations: | |
| (i) A company has a number of
employees. The attributes of EMPLOYEE include NAME, ADDRESS, and BIRTHDATE. The company
has also several projects. Attributes of PROJECT include CODE, DESCRIPTION and START DATE.
Each employee may be assigned to one or more projects, or may not be assigned to a
project. A project must have at least one employee assigned, and may have several
employees assigned.
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[3] | |
| (ii) A laboratory has several
chemists who work on various projects, and who may use certain kinds of equipment on each
project. Attributes of CHEMIST include NAME and PHONE NO. Attributes of PROJECT include
PROJECT ID and START DATE. Attributes of EQUIPMENT include NUMBER and COST.
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[3] | |
| (iii) A university has a large
number of course available. Attributes of a COURSE include NO, NAME and UNITS. Each course
may have one or more other courses as prerequisites, or may have no prerequisites.
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[3] | |
| (c) | In the Object-Oriented (O-O) model,
what is the difference between an object class and an object instance?
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[2] |
| (d) | Draw a O-O diagram to represent each of the following situations: | |
| (i) In a vehicle-licensing
application, there are three types of vehicle: passenger, truck and trailer. Vehicle ID is
an attribute of all vehicle types. Truck and trailer (but not passenger) vehicles have an
attribute named Gross Capacity. The passenger and truck types require a method named
PerformSmogCheck.
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[3] | |
| (ii) In a simple banking
application, there are exactly three types of account, with the following attributes: CHECKING Acct No, Date Opened, Balance, Service
Charge |
[4] |