How to Draw an Activity Diagram in UML
Activity diagrams aren't as difficult as they appear. If you can make a flowchart, you can create an activity diagram! Let's walk through the steps of how to draw an activity diagram in UML.
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SELECT A MEDIUM
You have several options for making activity diagrams, depending on your needs. Although pen and paper or a whiteboard can be used, we recommend a robust software program. Compared to their analog counterparts, digital activity diagrams are easier to edit, share, and store.
For the purposes of this guide, we’ll proceed as though you’re using Lucidchart. Our application has responsive, pre-built shapes and connectors, so they're simpler to style and rearrange. You can even add interactivity to your diagram and share it with others on your team for real-time collaborative editing.
IDENTIFY THE COMPONENTS
Activity diagrams are quite versatile, since they can model both business and computational systems and flows. Start by recording the steps of your process. Remember, activity diagrams can be used to:
- Demonstrate a software system's workflow
- Model applications with parallel processes
- Analyze a use case by showing the what and when of its actions
- Illustrate a complex sequential algorithm
If your use case fits one of these examples, it may be best modeled by an activity diagram.
ADD SHAPES AND SYMBOLS
Begin your chart by dragging out a start symbol—a black circle—from the toolbox. Then you can add activity shapes to the canvas and add your pre-written steps to each symbol; just double-click to add relevant text.
Drag out more symbols to reflect your workflow, and use arrowed lines to demonstrate the process flow of modeled activities. If you're not sure which symbols to utilize, see this guide for a complete overview of activity diagram symbols.
Activity shapes, or action shapes, reflect each major task that the user or system (or both) performs. To fill out the rest of the diagram, you need to know the direction of the control flow. This is modeled by connecting lines between shapes.
To show overlap among action shapes, use a synchronization bar with two or more connectors, which are either ingoing or outgoing depending on your flow. When your flow merges or branches out, a diamond symbol is utilized as the catalyst. The diamond, also called a decision shape, represents the triggering question or answer. An unlimited number of ingoing and outgoing paths may enter or leave the decision shape. To better define each path, you can drag out a text box or double click any line to enter text. These definitions are known as guards.
The aforementioned steps are usually sufficient for a simple activity diagram. However, other symbols may be used. For example, the note symbol can communicates messages that don't fit within the workflow itself. Again, to familiarize yourself with these shapes and meanings, check out this illustrated guide of activity diagram symbols.
REVIEW THE FLOW
To ensure that you're modeling everything correctly, it doesn't hurt to have your team members review the finished document. They'll have a fresh perspective that will assist you in spotting inefficiencies or inaccuracy.
Create beautiful diagrams online with Lucidchart. It's easy to collaborate with remote team members and implement changes fast. And with a variety of publishing options, sharing is simple.