UML basics: The class diagram - Part 1 - An introduction to the Unified Modeling Language

Oct 25, 2026

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UML basics: The class diagram provides an advanced introduction to UML 2 structure diagrams, with the class diagram as the core focus. It explains how structure diagrams represent the static structure of a modeled system, contrasting static relationships with behavioral diagrams that show dynamic interactions. The article clarifies the role of classifiers such as classes, interfaces, data types, and components, and outlines how this notation supports design validation and communication across analysts, architects, and developers.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages16

Reading Time40 min

AccessFree to download

The yin and yang of UML 2

Structure diagrams in general

The class diagram in particular

The basics

UML basics: The class diagram Page 1 of 16 © Copyright IBM Corporation 2004. [http://www-106.com/developerworks/rational/l](http://www-106.com/developerworks/rational/l)ibrary/content/RationalEdge/sep04/bell/index. html Search for: within All of dW Search help IBM home | Products & services | Support & downloads | My account developerWorks > Rational > UML basics: The class diagram An introduction to structure diagrams in UML 2 Level: Advanced Donald Bell IBM Global Services, IBM 15 Sep 2004 from The Rational Edge: As the most important example of the new structure diagram type in UML 2, the class diagram can be used by analysts, business modelers, developers, and testers throughout the software development lifecycle. This article offers a comprehensive introduction. This is the next installment in a series of articles about the essential diagrams used within the Unified Modeling Language, or UML. In my previous article on sequence diagrams, I shifted focus away from the UML 1.4 spec to OMG's Adopted 2.0 Draft Specification of UML (a.k.a. UML 2). In this article, I will discuss Structure Diagrams, which is a new diagram category that has been introduced in UML 2. Because the purpose of this series is to educate people about the notation elements and their meanings, this article focuses mainly on the class diagram. The reason for this will soon become clear. Subsequent articles will cover other diagrams included in the structure category. I also want to remind readers that this series is about UML notation elements, and that these articles are not meant to provide guidance on the best approach for modeling, or how to determine what things should be modeled in the first place. Instead, the purpose of this article and of the series in general is to help with a basic understanding of notation elements--their syntax and their meanings. With this knowledge you should be able to read diagrams and create your own diagrams using the proper notation elements. This article assumes you have a rudimentary understanding of object-oriented design. For those of you who need a little assistance with OO concepts, you might try the Sun brief tutorial about Object-Oriented The yin and yang of UML 2 Structure diagrams in general The basics Beyond the basics UML 2 additions Conclusion Notes About the author Rate this article UML basics: Part I: An introduction to the Unified Modeling Language UML basics: Part II: The activity diagram UML basics: Part III: The class diagram UML's sequence Diagram dW newsletters dW Subscription (CDs and downloads) The Rational Edge Programming at [http://java.sun.com/docs/books/tutorial/java/concepts/](http://java.sun.com/docs/books/tutorial/java/concepts/. Reading the sections)[.](http://java.sun.com/docs/books/tutorial/java/concepts/. Reading the sections)[ Reading the sections](http://java.sun.com/docs/books/tutorial/java/concepts/. Reading the sections) "What Is a Class?" and "What Is Inheritance?" should give you enough understanding to make this article useful. In addition, David Taylor's book, Object-Oriented Technologies: A Manager's Guide, offers an excellent, high-level explanation of object-oriented design without requiring an in-depth understanding of computer programming. The yin and yang of UML 2 In UML 2 there are two basic categories of diagrams: structure diagrams and behavior diagrams. Every UML diagram belongs to one these two diagram categories. The purpose of structure diagrams is to show the static structure of the system being modeled. They include the class, component, and or object diagrams. Behavioral diagrams, on the other hand, show the dynamic behavior between the objects in the system, including things like their methods, collaborations, and activities. Example behavior diagrams are activity, use case, and sequence diagrams. Structure diagrams in general As I have said, structure diagrams show the static structure of the

FAQs

What is the main purpose of UML structure diagrams in UML 2?

Structure diagrams show the static structure of the system being modeled, focusing on types and their instances irrespective of time.

How do structure diagrams differ from behavior diagrams in UML?

Structure diagrams convey static relationships among elements, while behavior diagrams show dynamic behavior between objects, such as methods, collaborations, and activities.

What types of elements does a UML class diagram typically model?

A UML class diagram commonly models classes, interfaces, data types, and components, which UML collectively calls classifiers.

Oct 25, 2026

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