Lab 12: Intro to UML

The Unified Modeling Language (UML) is a graphical language used to represent the structure and behavior of systems. While UML includes various diagram types for modeling different systems, we will focus on a specific subset related to visualizing classes and their relationships. UML serves as an effective communication tool, allowing teams to quickly convey the architecture and connections within a program through visual representations.

Here’s an example of a UML class diagram featuring multiple classes with an “inheritance” relationship:

§1 UML Class Diagram Overview #

A class diagram is a type of diagram that describes the structure of a system with a visual representation of its classes, attributes, methods, and the relationships among objects. A class diagram typically contains:

• Class Name: The name of the class.
• Attributes: The data members or properties of the class.
• Methods: The functions or operations that the class can perform.
• Access Specifiers: These define the visibility of the attributes and methods. Common access specifiers:
  • + for public
  • - for private
  • # for protected.

§2 Example Class #

Lets begin with a practical example. Here is a simple class prototype which represents a circle.

class Circle {
private:
    double radius;
    Point center;
    void myPrivateMethod();
public:
    void setRadius(double radius);
    void setCenter(Point center);
    double getArea();
    double getCircumference();
};

And here is how this Circle class would be represented in UML notation:

• The top compartment contains the name of the class. It is typically printed in bold and centered. It may also contain optional annotation text describing the nature of the class.
• The middle compartment contains the attributes (or data members) of the class. They are left-aligned.
• The bottom compartment contains the operations (or member functions) the class can execute. They are also left-aligned.
• All members show an access specifier on the far left of each member.

This class contains a member center which references another class, let’s add this Point class to the diagram:

Even without code, with the UML diagram we can effectively communicate that the Point class has two member variables: x and y. The solid line with a white diamond connecting the two classes signifies an aggregation relationship between them, indicating that the Point class is a part of the Circle class, but can exist independently of the Circle class.

§3 UML Diagram Relationships #

Relationships are used to show how different elements within a system interact with one another. Specifically, UML relationships are essential for modeling the connections between classes, objects, and other components in a system. the above example demonstrates an “Aggregation” relationship, there are several different types of relationships that can be represented in UML.

Common UML Relationships:

• Association: “relates to” (a general relationship, where one class is related to another, but both can exist independently)
• Inheritance: “is a” (the subclass is a specialized version of the parent class, inheriting its attributes and behaviors)
• Realization: “implements” (used to indicate that a class implements the behavior specified by an interface)
• Dependency: “uses” (a temporary relationship where one class depends on another, but they are not tightly coupled)
• Composition: “owns a” or “contains a” (a strong “has a” relationship where the part cannot exist independently of the whole; if the whole is destroyed, the part is destroyed too)
• Aggregation: “has a” (a weaker “has a” relationship where the part can exist independently of the whole)

Some more examples of each relationship type:

• https://creately.com/guides/class-diagram-relationships/
• https://blog.visual-paradigm.com/what-are-the-six-types-of-relationships-in-uml-class-diagrams

§4 UML Diagram Creation #

There are many online tools that can be utilized to create UML diagrams. Here is a non-exhaustive list of options for creating diagrams:

• diagrams.net - A free diagram creation tool
• lucidchart.com - Another visual diagram creator
• asciiflow.com - A visual editor for ASCII diagrams
• mermaid.live - Converts code-like text input into diagrams

I used mermaid.live for creating the diagrams in this lab. If you use this, you will want to first check the docs

§5 Further Reading #

• Textbook: Appendix F

§6 Assignment #

For this lab, you will create a few UML diagrams to visualize the following, be sure to include Access Specifiers and relationships in your diagrams:

Part 1:
Create a UML diagram representing the following Book class:

class Book {
private:
  std::string title;
  std::string author;
  std::string ISBN;
  double price;

public:
  // Method to display book information
  void getDetails();

  // Method to set a new price
  void setPrice(double newPrice);

  // Method to get the price
  double getPrice();
};

Part 2:
Design a UML class diagram for the following classes and relationships:

• A Teacher class that has public attributes name and subject, and a method teach().
• A Course class that contains a public courseName attribute and a courseDetails() method, as well as a reference to the Teacher class as a member.
• A Student class that has reference to a Course as a member, and additional attributes studentName and grade, and methods enroll() and viewGrade(). Be sure to use the correct relationships to link the classes together. Consider if the relationship between each class is a strong or weak connection, and if each class could exist without the others.

Write a short explanation of why you used a specific relationship for linking each class.

Part 3:
Create a UML class diagram for a Car class that has:

• Public Attributes: make, model, and year.
• A reference to an Engine class that has attributes type and horsepower, and a startEngine() method.
• References to a Tire class, with attributes brand and size, and a inflate() method. For this example, assume that the Tire and Engine classes cannot exist outside of a Car. This will affect the relationships between the classes.

Write a short explanation of why you used a specific relationship for linking each class.

For Submission: place all three diagrams and explanations on a document and submit as a single PDF.