Question

Consider the following relations for a database that keeps track of auto sales in a car dealership (Option refers to some optional equipment installed on an auto): cAR(Serial-No, Model, Manufacturer, Price) OPTIoNs(Serial-No, Option-Name, Price) sALEs(Salesperson-id, Serial-No, Date, Sale-price) sALEsPERsoN(Salesperson-id, Name, Phone) First, specify the foreign keys for this schema, stating any assumptions you make. Next, populate the relations with a few example tuples, and then give an example of an insertion in the SALES and SALESPERSON relations that violates the referential integrity constraints and of another insertion that does not.

Short answer

The foreign keys in this schema are 'Serial-No' in 'OPTIONS' and 'SALES' tables referencing 'Serial-No' in 'CAR' table, and 'Salesperson-id' in 'SALES' table referencing 'Salesperson-id' in the 'SALESPERSON' table. Violating referential integrity constraints could occur when trying to insert a record in 'OPTIONS' or 'SALES' tables for a 'Serial No' that does not exist in 'CAR' table or a record in 'SALES' table for a 'Salesperson-id' that doesn't exist in 'SALESPERSON'.

Step-by-step solution

Identify foreign keys

Foreign keys help to establish a connection between different tables in a database. In this case, \n1. 'Serial-No' in 'OPTION' and 'SALES' tables is a foreign key referencing 'Serial-No' in 'CAR' table, because the 'Serial-No' of a car should exist in the 'CAR' table before it can appear in the 'OPTION' and 'SALES' tables. \n2. 'Salesperson-id' in 'SALES' table is a foreign key referencing 'Salesperson-id' in the 'SALESPERSON' table. Therefore, for a sale to occur, the 'Salesperson-id' must firstly exist in the 'SALESPERSON' table.

Populate the relations with example tuples

As an example, let's add a few tuples into the tables. \n1. Into the 'CAR' table: ('SN-001', 'Model-1', 'Manufacturer-1', 10000)\n2. Into the 'OPTION' table: ('SN-001', 'Option-1', 1000) relates to the car from the 'CAR' table. \n3. Into the 'SALESPERSON' table: ('SP-001', 'Salesperson-1', '111-222-3333') \n4. Into the 'SALES' table: ('SP-001', 'SN-001', '2022-09-12', 9500) relates to both the car from the 'CAR' table and the salesperson from the 'SALESPERSON' table.

Examples of insertion that violates and does not violate the referential integrity constraints

According to the constraints identified in Step 1, it's clear that any attempt to create a record in 'SALES' and 'OPTIONS' tables for a 'Serial-No' that doesn't exist in the 'CAR' table would violate the constraints. Also, attempting to create a record in 'SALES' table with 'Salesperson-id' that doesn't exist in the 'SALESPERSON' table would break the constraints. \nOn the other hand, any additions that respect these conditions would not violate the constraints. For example, adding tuple ('SN-002', 'Model-2', 'Manufacturer-2', 15000) into the 'CAR' table and ('SP-002', 'Salesperson-2', '222-333-4444') into the 'SALESPERSON' table followed by related records in 'SALES' and 'OPTIONS' tables would maintain referential integrity.

Key concepts

Referential Integrity

In the context of a car dealership database, referential integrity is a crucial principle ensuring that relationships between tables stay consistent. It dictates that if one table refers to a key in another, the referred key must exist.

For example, every option or sale record refers to a specific car's serial number. If you try to enter an option or sale for a car serial number that doesn't exist in the car table, this would break the referential integrity. This principle prevents data anomalies and maintains the database's accuracy, avoiding situations where an optional equipment or sale is recorded against a non-existent car.

Think of it like this: if you were told that a specific piece of equipment was installed in a ghost car, it wouldn't make sense, right? Referential integrity ensures that every piece of equipment is accounted for in a real, registered car.

Relational Database Design

Relational database design is the process of organizing data into a series of tables or relations with unique keys identifying each row, which is what we see in the structure of our car dealership database.

The car table, for instance, uses the serial number as a unique identifier, ensuring that each entry, or 'tuple', represents one and only one vehicle. This design is all about creating relations that are simple, intuitive, and able to accurately describe the real-world relationships between data entities, like salespeople, cars, and sales.

An effective design assists in keeping data organized, allowing for smooth and reliable data retrieval, and simplifies the addition of new data while maintaining data integrity. A well-structured relational database is a keystone of any system requiring data that's easy to manage and analyze.

Primary and Foreign Key Constraints

When we talk about keys in a database, we are referring to attributes that play a specific role. Primary keys are unique identifiers within a table, ensuring that each record is distinct. For the 'CAR' table, 'Serial-No' is an example of a primary key.

Foreign keys, on the other hand, are used to create a link between tables. They reference primary keys in another table to establish a relationship. In our example database, 'SALES' and 'OPTIONS' have a foreign key constraint on 'Serial-No', connecting them back to the 'CAR' table.

With these constraints in place, the database system checks to ensure that every foreign key matches an existing primary key in the referenced table, upholding referential integrity. These constraints are the gatekeepers that prevent discordant data from creeping in, such as an option or sale tied to a non-existent car or salesperson.