Class Diagram Example: Understanding Relationships


This is a simple class diagram example that shows the use of associations in relating classes. Different multiplicities are set to the association roles to indicate the cardinality of elements.

You can create your own Class diagram by editing this one. Simply Click Use this Template to start, or click Create Blank to create a new one.

What is Class Diagram?

The class diagram is an important part of the UML, as it captures the static view of the system. The class diagram models classes in the real world and specifies the relationships between them. A class is essentially a template from which any number of objects can be derived. It does not exist as an object in its own right, but it defines the properties (or attributes) that an object will have, and the operations that can be performed by the object. We can also use packages represent groups of related classes and relationships.

How to draw Class Diagram?

The following guideline should be consider while developing a class diagram -

  • Use meaningful name for a class to describe the aspect of the system.
  • If you are involved in a large organization, it is better to refer to the glossary for existing class for reuse and to avoid it end up to be many variants for similar classes that serve the same purpose in the repository
  • Responsibility (attributes and methods) of each class should be clearly identified only in the detailed design phase and it is not necessary to do it in upfront.
  • Refine and elaborate your class model in just-in-time manner and do not rush every detail in the upfront.
  • You don't have to include all classes in one single class diagram, for example, include only the group of classes that participate in a use case scenarios and no others.
  • Reuse classes by use master view and auxiliary view among different class diagrams.
  • You can also avoid cross relationship link between classes by using auxiliary view of the same class to be appeared within the same class diagram.
  • Package related classes together to enforce software architecture and best practice such as MVC framework.

Why do we need Class Diagram?

Class diagrams are useful in many stages of system design:

  1. Analysis stage - a class diagram can help you to understand the requirements of your problem domain and to identify its components.
  2. Design stage - you can refine your earlier analysis and conceptual models into class diagrams that show the specific parts of your system, user interfaces, logical implementations, and so on.v
  3. Detailed design stage - the class diagrams that you create during the early stages of the project contain classes that often translate into actual software classes and objects when you write code.v
  4. Implementation stage - you can use class diagrams to convert your models into code and to convert your code into models.

Your class diagrams then become a snapshot that describes exactly how your system works, the relationships between system components at many levels, and how you plan to implement those components.

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