This chapter does not have any technical requirements. In order to create UML diagrams, the following open source software tool is recommended:

• Modelio, which is available at https://www.modelio.org

Modelio can be run on systems with any of the following operating systems:

• Debian/Ubuntu
• macOS X
• RedHat/CentOS
• Windows 7
• Windows 8
• Windows 10

UML was developed in 1994 to document object-oriented systems. Since that time, UML has become a standard tool for software engineers, software developers, and businesses. UML is used to design software and, after programming, also provides a visual record for the system which can be included as part of formal software documentation.

There are two types of UML diagrams—behavioral and structural. Both are described in the sections that follow.

Behavioral diagrams illustrate how system components interact to form a system. The four diagrams listed here are behavioral, and are briefly described in the subsections that follow:

• Activity diagrams
• Interaction diagrams
• State machine diagrams
• Use case diagrams

Activity diagrams illustrate the flow of processes in a system. This type of diagram is used to visually document activities within a system, also referred to as a system's procedures or dynamic components.

The following activity diagram shows the activities involved when a coffee shop customer places an order. The starting point is the top black circle. From there, an order is received. Beneath the Receive...

Structural diagrams illustrate components of a system. The six diagrams listed here are structural, and are briefly described in the subsections that follow:

• Class diagrams
• Component diagrams
• Composite structure diagrams
• Deployment diagrams
• Object diagrams
• Package diagrams

The class diagram is the most commonly used UML diagram, as it provides a visual description of a system's objects. Consider that, in Java, everything is an object, so you can see the relevance and reason as to why this particular diagram is so widely used. Class diagrams do more than just display objects—they visually depict their construction and relationships with other classes.

As you...

The Universal Modeling Language (UML) is used to create visual documentation of our systems. This can be used to design a system as well as document a system. UML is widely used by software engineers, software developers, and other professionals.

Two of the 14 UML diagrams are behavioral and structural. Behavioral diagrams illustrate how system components interact to form a system and include activity diagrams, interaction diagrams, state machine diagrams, and use case diagrams. There are several types of interaction UML diagrams, including sequence diagrams, communication diagrams, and timing diagrams.

Structural diagrams illustrate components of a system and include class diagrams, component diagrams, composite structure diagrams, deployment diagrams, object diagrams, and package diagrams.

In the next chapter, Object-Oriented Design Patterns, we will explore intermediate...

1. What are the two basic types of UML diagrams?
2. Why was UML initially created?
3. List four behavioral UML diagrams.
4. Which UML diagram provides a system's process flow?
5. Which UML diagram documents the interactions between a system and its users?
6. What is a UML actor?
7. What type of UML diagram illustrates system components?
8. What is the most commonly used UML diagram?
9. Which UML diagram shows the runtime structure of a system?
10. Which UML diagram visually documents a system's hardware and software?

• UML 2.0 in Action: A project-based-tutorial (https://www.packtpub.com/hardware-and-creative/uml-20-action-project-based-tutorial)