Question

Consider a company that owns and operates parking lots. Draw an ERD to include the following specifications. Each parking lot has a unique address (use the typical fields for addresses) and each parking lot has a certain number, say n, of parking spaces. Each space in a lot has a number between 1 and n. The cost of renting a parking space is the same for all spaces in a lot. The company rents individual spaces out to its customers. Each customer is identified by a driver’s license id, has a first and last name. Each customer will identify possibly several cars that they will park in the space rented to them. For each car the company needs to know the year, make, model, colour and its license plate number.

Short answer

The ERD should include four entities ('Parking Lot', 'Parking Space', 'Customer', 'Car'), each with its specific attributes. The relationship among them should be represented in accordance to the given specifications.

Step-by-step solution

Identifying Entities

The first step is identifying the entities. In this case, the entities are 'Parking Lot', 'Parking Space', 'Customer' and 'Car'.

Identifying Attributes

The second step is identifying the attributes for each entity. 'Parking Lot' has attributes 'Address' and 'Number of Spaces', 'Parking Space' has attributes 'Space number' and 'Rental Cost', 'Customer' has attributes 'Driver’s License ID', 'First Name', 'Last Name'. 'Car' has attributes 'Year', 'Make', 'Model', 'Color', and 'License Plate Number'.

Identifying Relationships

The third step is identifying the relationships between these entities. 'Customer' rents 'Parking Space'. 'Customer' identifies 'Car'. The relationship between 'Parking Space' and 'Parking Lot' could be represented as 'Parking Space' is located in 'Parking Lot'.

Draw the ERD

Based on the relationships and attributes, draw the ERD. Each entity should be represented as a rectangle and its attributes as ellipses connected to the rectangle. Relationships should be represented as diamonds connecting the related rectangles with lines.

Key concepts

Database Design

Database design is the process of meticulously organizing and structuring data into a database system. The goal is to create a database that is both efficient and scalable, catering effectively to the needs of users and applications. The basic foundation of database design involves building an Entity-Relationship Diagram (ERD) which depicts data's structure visually. This diagram assists in conceptualizing data flows and interactions.

In our scenario, we are dealing with a company that owns parking lots and rents out parking spaces. The ERD will represent key data elements of this situation and illustrate how they are interconnected. A well-conceived ERD not only captures the essence of the business model but also simplifies the database construction and future development processes.

Entity Identification

Entity identification is a crucial step in constructing a robust ERD and involves pinpointing the principal components, or 'entities', within the business model. An entity is typically an object or concept that holds data in the real world.

For instance, in the parking lot company example, the identified entities include:

• Parking Lot: Represents each distinct parking facility.
• Parking Space: Refers to each slot available for rent within a parking lot.
• Customer: The individuals renting parking spaces.
• Car: The vehicles parked by customers.

Identifying these entities is fundamental as it lays the groundwork upon which the database is designed, ensuring that all necessary data components are included.

Attributes and Relationships

Once entities are identified, the next task is defining their attributes and relationships. Attributes are characteristics that describe or qualify an entity, while relationships show how entities interact with one another in a database context.

Each entity in our parking lot example has specific attributes:

• Parking Lot: Address, Number of Spaces.
• Parking Space: Space Number, Rental Cost.
• Customer: Driver’s License ID, First Name, Last Name.
• Car: Year, Make, Model, Color, License Plate Number.

When it comes to relationships:

• A Customer rents a Parking Space.
• A Customer can identify one or more Cars.
• A Parking Space is located in a Parking Lot.

Understanding these attributes and relationships is essential as it ensures clarity in data interactions and integrity in the database design.

ERD Drawing Steps

Creating the Entity-Relationship Diagram (ERD) involves several methodical steps that transform identified data into a visual map. Each step builds upon the last to shape a comprehensive ERD.

Here is a streamlined version of the process:

• Step 1: Identify Entities - Start by recognizing key components like Parking Lot, Parking Space, Customer, and Car.
• Step 2: Define Attributes - Enumerate characteristics pertinent to each entity, ensuring all data points are noted for completeness.
• Step 3: Determine Relationships - Chart out how each entity interacts, outlining connections such as Customer-to-Parking Space leases.
• Step 4: Draw the ERD - Represent each entity with rectangles, attributes with ellipses connected to their respective entities, and relationships with diamonds to clarify the flows between them.

By following these steps, you create a powerful visual representation that aids in the development and management of the database, ensuring it meets functional requirements effectively.