Question

Create a database model according to the following steps: Create a simple class diagram containing three classes: Vehicle, Car, and Truck. Provide two attributes for each of these three classes. Create a rough sketch of a relational table that will store the objects belonging to the aforementioned three classes. Ensure you have tried all three options—single table, two tables, and three tables—in your database design. Enter two objects per table, corresponding to the classes. Use the two-table design to recreate a Car object. Repeat the preceding step to recreate a Truck object. Create a simple association relationship in a separate class diagram showing Driver and Car. Apply a multiplicity of 1 on the driver side and N on the Car side. Add/modify your table designs to handle storing of two objects belonging to Car and two belonging to Driver. Modify the multiplicity on the Driver side to N. This makes it a many-to-many multiplicity. Modify your table designs to handle this multiplicity and show where and how the KEYS or IDs will have to be placed. Create a class diagram corresponding to the tables you have designed. Stereotype all classes on that class diagram as <>. For each diagram, ensure you are providing a 1-2 page critical analysis that demonstrates your interpretation and integration of the material.

Answer 1

A database model for Vehicles includes class diagrams for Vehicle, Car, and Truck with associated attributes and a variety of tables (single, two, or three tables) to store their data. A join table is used for the many-to-many relationship between Driver and Car. Class diagrams are then aligned with these tables to reflect the database structure.

Step-by-step explanation:

Designing a Database Model for Vehicles

To design a database model for vehicles, we start by creating class diagrams for three entities: Vehicle, Car, and Truck. Each class could have two attributes; for example, Vehicle might have 'make' and 'model', Car could have 'number_of_doors' and 'is_electric', and Truck might include 'cargo_capacity' and 'number_of_axles'. Considering our storage options, we can design the database using one, two, or three tables to accommodate the hierarchical structure of these classes.

Single Table Inheritance

In a single table design, a single table holds all properties and includes a type attribute to differentiate the vehicle types. This design often contains many null fields and can become complicated as the specialization hierarchy grows.

Class Table Inheritance

A three-table design has one table for Vehicle and separate tables for Car and Truck, where each subclass table inherits the primary key from the Vehicle table, ensuring referential integrity and minimizing nulls.

Concrete Table Inheritance

A two-table design splits the data into relevant subclass tables, which means, for our case, we have one table for Car and one for Truck. These tables include shared attributes and their unique attributes.

Association Relationship

To represent the relationship between Driver and Car, we need an additional table to handle the many-to-many relationship resulting from modifying the multiplicity. This table, called a join table, will contain foreign keys referencing both the Driver and Car entities.

Final Class Diagram

Finally, the class diagram corresponding to our table design should represent all the entities marked as <> classes, depicting the structure of the database as well as the relationships between tables.