Question

A vehicle database contains information about cars (identified by Vehicle Identification Number, or VIN) and Drivers (identified by Civil Ids). Drivers own vehicles; each situation concerns the Owns relationship set. For each situation, draw an EER diagram that describes it (assuming no further constraints hold).

1. Drivers can own vehicles for an extended period, and each owned vehicle must be recorded, including when it was added to their possession and when it left their possession.
2. Driver can own several vehicles simultaneously, and only what the driver currently owns is recorded. (Assume this condition applies in all subsequent questions.)
3. Every driver must own at least one vehicle.
4. Every driver owns exactly one vehicle (no more, no less).
5. Every driver teaches exactly one vehicle (no more, no less), and every vehicle must be owned by some driver.
Note: In (5), ‘some driver’ refers to ‘one driver’!
6. Rephrase (6) as follows: Suppose that a certain vehicle can be owned by a team of drivers jointly. Model this situation by introducing additional entity sets and relationship sets if necessary. Here, we assume that only the latest owners of a vehicle need to be recorded.

Answer 1

This detailed answer explains how to draw an EER diagram to represent various situations related to the ownership of vehicles by drivers.

Step-by-step explanation:

1. Drivers can own vehicles for an extended period, and each owned vehicle must be recorded, including when it was added to their possession and when it left their possession.

To represent this situation in an EER diagram, you would include a relationship set named 'Owns' between the 'Drivers' entity set and the 'Vehicles' entity set. The 'Owns' relationship set would have attributes such as 'Start Date' and 'End Date' to record when a driver added a vehicle to their possession and when they no longer owned it.

2. Driver can own several vehicles simultaneously, and only what the driver currently owns is recorded.

For this situation, you would still have the 'Owns' relationship set between 'Drivers' and 'Vehicles'. However, you would need to include a 'Currently Owns' attribute in the 'Owns' relationship set to keep track of only the vehicles that the driver currently owns.

3. Every driver must own at least one vehicle.

In the EER diagram, you would enforce this constraint by making the 'Owns' relationship set a total participation relationship set, meaning that every driver must participate in the 'Owns' relationship set.

4. Every driver owns exactly one vehicle (no more, no less).

To represent this constraint, you would make the 'Owns' relationship set a one-to-one relationship set between 'Drivers' and 'Vehicles'. This means that each driver can own exactly one vehicle.

5. Every driver teaches exactly one vehicle (no more, no less), and every vehicle must be owned by some driver.

In this case, you would include a relationship set named 'Teaches' between 'Drivers' and 'Vehicles' to represent the teaching relationship. The 'Teaches' relationship set would also be a one-to-one relationship set, ensuring that each driver teaches exactly one vehicle. Additionally, the 'Owns' relationship set would be a total participation relationship set to ensure that every vehicle must be owned by some driver.

6. Rephrase (6) as follows: Suppose that a certain vehicle can be owned by a team of drivers jointly. Model this situation by introducing additional entity sets and relationship sets if necessary. Here, we assume that only the latest owners of a vehicle need to be recorded.

In this situation, you would introduce an additional entity set called 'Joint Owners'. The 'Owns' relationship set would then connect 'Drivers' and 'Joint Owners', indicating that a vehicle can be jointly owned by a team of drivers. To record only the latest owners of a vehicle, you would need to add an attribute such as 'Latest Owner' in the 'Owns' relationship set.