Question

Consider a company that owns and operates parking lots. Develop an ERD with two entity types Parking Lot and Space and where: The address of a parking lot serves to identify the lot. Each space within a lot is rented at the same monthly rental charge. Each parking space is known by its number within the lot (within a lot these always start at 1). Each parking space is rented out to at most one vehicle. The vehicle’s identifier must be recorded. The identifier comprises a province code and license plate number.

Short answer

The ERD for the parking lot scenario has three entities: Parking Lot, Space, and Vehicle. Parking Lot has an attribute 'Address' which is a key. Space has attributes 'Number' and 'Rental Charge', with 'Number' acting as a key. There's a one-to-many relationship from Parking Lot to Space and a one-to-one relationship from Space to Vehicle. Vehicle's identifier, made up of 'Province Code' and 'License Plate Number' and specific to each Space, must be recorded.

Step-by-step solution

Identify Entities

Entities can be objects or concepts that are describable and identifiable. From the exercise, the entities we have are 'Parking Lot' and 'Space'.

Identify Attributes

Attributes are properties or characteristics of entities. For the 'Parking Lot' entity, the attribute is 'Address', which also serves as a unique identifier (i.e., a key). For the 'Space' entity, the attributes are 'Number' and 'Rental Charge'. As described, each 'Space' is identified by a unique 'Number' within a 'Parking Lot'.

Identify Relationships

Relationships connect entities. In this exercise, we're given that each 'Parking Space' is rented out to at most one 'Vehicle'. Thus, a 'Vehicle' is another entity, and the relationship between 'Space' and 'Vehicle' is a one-to-one relationship. The 'Vehicle' entity has an identifier made of 'Province Code' and 'License Plate Number'.

Draw ERD

Draw the ERD with 'Parking Lot', 'Space', and 'Vehicle' as entities. Include attributes for each entity and mark their keys. Show the relationships between entities: one-to-many from 'Parking Lot' to 'Space', as there can be multiple spaces in a parking lot, and one-to-one between 'Space' and 'Vehicle', as a space can be rented to at most one vehicle. The relationship between 'Space' and 'Vehicle' should also indicate that the vehicle's identifier must be recorded.

Key concepts

Data Modeling

Data modeling is a crucial step in creating a structured, efficient database. It involves the process of defining and organizing data elements and their relationships. In our exercise, we consider entities like 'Parking Lot' and 'Space'. Each of these entities needs a clear representation in the data model.

• **Entities**: Key objects like `Parking Lot` and `Space` are essential elements in our model. In data modeling, entities are the objects whose data we need to track.
• **Attributes**: These are characteristics or properties of entities. In this case, `Address` for `Parking Lot`, and `Number` and `Rental Charge` for `Space` are attributes. They help in further detailing each entity.
• **Keys**: Unique identifiers for entities, such as the parking lot's address, help ensure each entity can be uniquely identified and linked.

Breaking down data into identifiable pieces facilitates clearer understanding and communication of a system's structure. It also lays the groundwork for database design.

Database Design

Database design is the next step after data modeling, where the model is implemented into an actual database. A well-designed database improves efficiency and performance in data handling. **Key Steps in Database Design:**

• **Defining Tables**: Each entity from the data model becomes a table in the database. For example, `Parking Lot` and `Space` become individual tables.
• **Choosing Data Types**: Assign appropriate data types to each field in the table. For instance, the `Address` might be a string, while `Rental Charge` could be a decimal or float.
• **Establishing Primary and Foreign Keys**: The `Address` as a primary key in `Parking Lot` ensures each entry is unique. In `Space`, the `Number` combined with `Lot ID` can serve as a composite primary key. Foreign keys help establish relations between tables.

Creating a strong database design ensures that data integrity is maintained and operations on data are optimized. It is a critical step that reflects the earlier data model into a usable form.

Relationship Types

In database design, relationship types describe how entities associate with one another, impacting data organization and retrieval. **Understanding Relationship Types:**

• **One-to-Many**: One instance of an entity is related to multiple instances of another. In our exercise, one `Parking Lot` can have many `Spaces`. This is typical for hierarchical data structures.
• **One-to-One**: Each instance of an entity is related to one and only one instance of another entity. A `Space` is rented to at most one `Vehicle`, demonstrating a one-to-one relationship.

These relationships inform how tables are linked in a database through keys. Understanding these types allows one to anticipate how data should be accessed and linked, ensuring efficient data retrieval and storage patterns.