UML Activity Diagram Tutorial


UML is very handy but the terminology can be somewhat overwhelming for someone unfamiliar. In UML, an activity diagram is nothing more than a flowchart. It’s a simple standardized system of notations for a flowchart.

What is an activity diagram?

The Unified Modeling Language has several subsets of diagrams that it can model, including structure diagrams, interaction diagrams, and behavior diagrams. Activity diagrams are a subset of the latter. Along with use case and state machine diagrams, activity diagrams are used to describe the functionalities of business activities and software systems. You'll use a set of specialized symbols—including those for starting, ending, merging, or receiving steps in the flow—to make an activity diagram, which we’ll cover more in depth within this activity diagram guide.

Stakeholders have many issues to manage, so it's important to communicate with clarity and brevity. Activity diagrams help people on the business and development sides of an organization come together to understand the same process and behavior.

Benefits of activity diagrams

Making an activity diagram can have a number of benefits to users. Consider creating an activity diagram to:

  • Demonstrate the logic of an algorithm.

  • Describe the steps performed in a UML use case.

  • Illustrate a business process or workflow between users and the system.

  • Simplify and improve any process by clarifying complicated use cases.

  • Model software architecture elements, such as method, function, and operation.

Basic components of an activity diagram

Before you begin making an activity diagram, you should first understand its makeup. Some of the most common components of an activity diagram include:

  • Actions - a step in the activity wherein the users or software perform a given task. In Lucidchart, this is symbolized with a round-edged rectangle.

  • Decision node - a conditional branch in the flow that is represented by a diamond. It includes a single input and two or more outputs.

  • Control flows - this is another name for the connectors that show the flow between steps in the diagram.

  • Start node - symbolizes the beginning of the activity. This is represented by a black circle.

  • End node - represents the final step in the activity. It's modeled with an outlined black circle.

Activity diagram symbols

These activity diagram shapes and symbols are some of the most common types you'll find in most UML diagrams.

 

Symbol Name Description

start Symbol

Start symbol

Represents the beginning of a process or workflow in an activity diagram. It can be used by itself or with a note symbol that explains the starting point.

activity Symbol

Activity symbol

This is the main building blocks of an activity diagram. These shapes indicate the activities that make up a modeled process with a short description.

connector Symbol

Connector symbol

Represented by arrowed lines that show the directional flow, or control flow, of the activity. An incoming arrow starts a step of an activity; once the step is completed, the flow continues with the outgoing arrow.

joint Symbol

Joint symbol/ Synchronization bar

A thick vertical or horizontal line. It combines two concurrent activities and re-introduces them to a flow where only one activity occurs at a time.

fork Symbol

Fork symbol

Symbolized with multiple arrowed lines from a join. It splits a single activity flow into two concurrent activities.

decision Symbol

Decision symbol

Diamond shaped UML symbol representing a decision and always has at least two paths branching out with condition text to allow users to view options. It represents the branching or merging of various flows with the symbol acting as a frame or container.

note Symbol

Note symbol

Allows the diagram creators or collaborators to communicate additional messages that don't fit within the diagram itself. Leave notes for added clarity and specification.

send signal Symbol

Send signal symbol

Means that a signal is being sent to a receiving activity.

receive signal Symbol

Receive signal symbol

Demonstrates the acceptance of an event. After the event is received, the flow that comes from this action is completed.

shallow history pseudostate symbol

Shallow history pseudostate symbol

Represents a transition that invokes the last active state.

option loop symbol

Option loop symbol

Allows the creator to model a repetitive sequence within the option loop symbol.

flow final symbol

Flow final symbol

Use this UML symbol to represent the ending point of a specific process' flow. This shouldn’t represent the end of all flows in an activity, which the End Symbol represents. This symbol should be placed at the end of a process in a single activity flow.

condition text

Condition text

Condition text is placed next to a decision marker to let you know under what condition an activity flow should split off in that direction.

end symbol

End symbol

This is the UML symbol for the end state of an activity and represents the completion of all flows of a process.

Activity diagram examples

Utilizing an activity diagram to map out process flows is easy and can be especially useful. Consider the two examples below when it comes to creating UML activity diagrams.

Activity diagram for a login page

This activity diagram shows the process of logging into a website, from entering your username and password, to successfully logging in to the system. Login is a fundamental part of day-to-day life, whether it’s for banking sites, online shopping, or checking email. Lucidchart is the ideal tool for creating any kind of UML flowchart, whether it’s an activity diagram, a use case diagram, or a component diagram. This login diagram uses different container shapes for activities, decisions, and notes. Lucidchart offers in-editor collaboration tools and instant web publishing.

activity diagram example

Click here to use this template

Activity Diagram for a banking system

This diagram shows the process of either withdrawing or depositing money into a bank account. An advantage of representing the workflow visually in UML is the ability to show withdrawals and deposits on one chart. When you use Lucidchart to build an activity diagram, you can customize your templates with professional-level typefaces, colors, and arranging options. Never worry about losing your documents with secure, cloud-based storage.

activity diagram template

Click here to use this template

How to make an activity diagram

In Lucidchart, creating an activity diagram from scratch is surprisingly simple.

  1. Open a blank document or start with a template and enable the UML shape library.

  2. Select the shape you want and drag out symbols from the toolbox to the canvas

  3. Then model the process flow by drawing lines between shapes.

Dive deeper into this guide on how to draw an activity diagram in UML for additional insight. It's easy to resize and style any element. You can even import SVG shapes and Visio files for a custom solution. If you'd like to learn more about UML, check out our What is UML tutorial.