Software Development Diagrams - Class diagram
Tags: diagrams, softwaredevelopment, beginners, programming
Published: 2023-10-01 19:53:55

In this article, we will cover what a class diagram is, which are the key terms for using it, and in the end we will use the [base exercise](https://dev.to/alicefolvaiter/software-development-diagrams-base-exercise-mpk) in order to create a class diagram. 

A class diagram is a graphical representation that helps us understand the structure of a software application. Think of it as a visual guide that outlines what each part of the code does and how different parts relate to each other. It's an invaluable tool for planning and designing software systems, making it easier for developers to collaborate and build complex applications.

There are a lot of resources that cover all the details of a class diagram, so I will iterate throw the main components with a short explanation. I will recommend [this website](https://www.visual-paradigm.com/guide/uml-unified-modeling-language/uml-class-diagram-tutorial/) to learn more about class diagrams.

Here are the key components of a class diagram explained by a software developer:

1. **Class**: Think of it as a template for an object in your program.
2. **Attributes (Variables)**: These are the characteristics or data that each object of a class will have.
3. **Methods (Functions)**: Methods are the actions or behaviors that objects of a class can perform. 
4. **Associations**: This shows how classes are connected or related to each other. 
5. **Aggregation:** Aggregation is like saying one thing is made up of smaller parts. It's a way to show that a bigger thing, called the "whole," contains smaller things, called "parts," but the parts can exist on their own as well.
6. **Inheritance (Generalization)**: Inheritance is like saying one class is a more specialized version of another.
7. **Dependency**: This is when one class relies on another class in some way, like when a class uses the methods or attributes of another class. It's like showing that one class needs another to work correctly.
8. **Interfaces**: An interface defines a set of methods that a class must implement. It's like setting a contract that says, "If you want to be this type of class, you have to do these things." It helps ensure consistency in your code.
9. **Composition:** A special type of aggregation where parts are destroyed when the whole is destroyed.
10. **Package**: Think of a package as a way to organize related classes. It's like putting classes that work together in a folder. Packages make it easier to manage large projects.

Now let’s create the class diagram for **MyDoctor** application. Having in mind the base exercises that we added in [this article](https://dev.to/alicefolvaiter/software-development-diagrams-base-exercise-mpk), we will create the class diagram for it. This diagram was created using [LucidChart](https://lucid.app/lucidchart).

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/kzv921brhq0op1fhe49s.png)

Reading this diagram we can see the classes with the main attributes and methods: User, Doctor, Patient, Office, Schedule, Appointment, BloodTest, Consultation, Surgery.

For the relationships we have the following:

- Doctor and Patient inherits User since they are specialized users in the application
- Doctor aggregates Schedule because the Doctor has a list of schedules
- Office aggregates Schedule because the Office has a list of schedules
- Patient aggregates Appointment because the Patient will have a list of schedules
- BloodTest, Consultation and Surgery inherits Appointment
- Appointment has a composition relationship with Schedule because an appointment cannot exist without a schedule

Tools for class diagrams: [LucidChart](https://lucid.app/lucidchart), [App Diagrams](https://app.diagrams.net/), [](https://icepanel.io/)[Creately](https://creately.com/diagram-type/class-diagram/), [Lucid](https://lucid.app/), [SmartDraw](https://www.smartdraw.com/), [Visual-Paradigm](https://online.visual-paradigm.com/app/diagrams/), [Creately](https://creately.com/).

Class diagrams are a valuable tool for software developers because they provide a clear visual representation of the software's structure, making it easier to design, communicate, and understand complex systems. These components allow developers to define the building blocks of their software and the relationships between them.