Question

EER diagram

Draw the EER diagram for the following systems.

Persons in an organization are employees or customers or visitors. Employees have computers.
The IT department of the company builds all its computers from components. Each computer
consists of several components like graphic cards, network cards, mother boards, memory
capsules, hard discs, etc. When a component is bought from a supplier it is given an ID number.
The finished computer is placed in a room, which may contain several computers.
Prepare an EER diagram using only the concepts listed above, that shows, as necessary,
entities, relationships, specializations and generalizations. Show the most likely cardinalities
(min, max) for all relationships.

Answer 1

Diagram:

(i) The above enhanced entity relationship diagram is completely based upon the requirements mentioned in the case study. There are total of eight entities in the diagram including the specialization entities and they are as follows:

a. Person

b. Customer

c. Visitor

d. Employee

e. Computer

f. Component

g. Supplier

h. Room.

(ii) The person in the organization is described as a separate entity which is specialized with three entities -visitors, customers, and employees. Employees have computers. From the information provided, it can be assumed that each employee has one computer assigned to them. So the relationship has between the computer and person entity and the cardinality of the relationship is one to one or 1:1.

(ii) Each computer consists of several components where the component is an individual entity in the diagram and the relationship between them is consists_of. As a particular computer may build with several components so the cardinality of the relationship from computer entity one to many or 1:M.

(iii) Components are supplied by the supplier from which the component gets an id number so the ID number will be an attribute of the entity component. A Supplier supplies many components to the IT department. The relationship between these two entities is supplies and the cardinality is one to many or 1:M.

(iv) The relationship placed_in denotes the room entity having several computers. As the last line suggests in the case study that "which may contain several computers" the cardinality of the relationship is many to one from computer entity side.