Exam-style question
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A community equipment service needs a conceptual data model. It stores details of customers and equipment. A customer can make several hires over time. Each hire is for one customer and one piece of equipment. The service must record the hire date and return date. Produce entity descriptions, identify the entity identifiers, and describe an appropriate entity relationship diagram.
Model answer
What a good answer should say
- Customer (CustomerID, CustomerName, CustomerAddress) Equipment (EquipmentID, EquipmentDescription, EquipmentCondition) Hire (HireID, HireDate, ReturnDate, CustomerID, EquipmentID) Customer is related to Hire because a customer can make several hires.
- Equipment is related to Hire because a piece of equipment can occur in several hire records over time.
- Each Hire is associated with one Customer and one Equipment item.
- CustomerID, EquipmentID and HireID are the entity identifiers and would be underlined in the entity descriptions or identified as the identifiers in the diagram.
Explanation
Why this works
The requirements describe three different entities: customers, equipment and individual hires. Hire is needed because the dates belong to a particular borrowing event, not permanently to a customer or an equipment item.
Including CustomerID and EquipmentID in Hire makes the two relationships explicit in the conceptual model.
Common mistake
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