UML Sequence Diagram

UML Sequence Diagram Template

Understand the order in which the events within a sequence interact with each other.

About the UML Sequence Diagram Template

A sequence diagram is a tool that depicts object interaction in a system in sequential order. Teams use the diagram to get a better overview of their work processes.

Keep reading to learn more about our UML Sequence Diagram Template.

What is a sequence diagram?

A sequence diagram is a Unified Modeling Language (UML) diagram that showcases the interactions between the objects in a system in sequential order. It is a type of interaction diagram, and it’s also referred to as a UML sequence diagram.

You can use a system sequence diagram to map the customer journey through an eCommerce store or to get a high-level overview of specific business functions.

In the first scenario, the customer is the "actor" or external entity that interacts with the elements of the diagram. The diagram for the second example does not necessarily need to have an "actor."

Teams can use this diagram to analyze existing work systems. 

However, one of its primary use cases is in requirements documents for future systems implementation. So, when staff or analysts are designing a new system, one or more sequence diagrams are used to showcase how this system will behave.

Benefits of a sequence diagram

Let’s walk through four benefits of a sequence diagram.

1. Discover interface and logical problems early 

Since creating a sequence diagram requires teams to flesh out all the details of a system, it helps them find problems well before the implementation phase.

2. Use it as a collaboration tool

A sequence diagram is an excellent option when you want to clearly depict how a system works or should work during team meetings or projects. Because of this, you can use it as a collaboration diagram.

3. Get a bird’s-eye view

With a sequence diagram, analysts can examine a system, whether that's a shopping kiosk or a new app, at various levels of abstraction. You can start with a high-level view of the system and then delve into the details as required.

4. Update it easily

Teams can update every element within a sequence diagram to match changing events or circumstances without overhauling the entire diagram.

How to use the Sequence Diagram Template

Our whiteboard tool enables teams to effortlessly create and share their own sequence diagrams. Start by selecting the Sequence Diagram Template and then follow these steps:

Step 1: Identify your lifelines. Lifelines represent the roles or object instances that are interacting. There can be two or more lifelines in a sequence. Each lifeline is placed in a box at the top of the diagram and has a vertical dashed line below it.

Step 2: Create messages. A message is an interaction between the lifelines. It is represented using a horizontal arrow. Seven different types of messages can be used in a sequence diagram.

Step 3: Define your actor. An actor is an external entity that interacts with the sequence but is not a part of that sequence. In online shopping, for example, the "actor" is the customer, while the shopping system (e.g. "Add to cart"-"Total"-"Confirm order") is the sequence.

Step 4: Add action bars. An activation bar is a thin rectangle that is placed under a lifeline to represent the time it takes to complete a task. You can add multiple activation bars on the lifelines.

Step 5: Include any other important features. In complex sequence diagrams, you can add Alternatives, Options, and Loops to represent different sequences.

Examples of a sequence diagram

Let's use the example of a fast-food restaurant's ordering system to understand how a sequence diagram works.

The following interactions take place during this sequence when a customer wants to place an order:

  • They go to the cash counter and place an order

  • The cashier confirms the order and gives order details to the kitchen

  • The kitchen staff prepare the food and deliver it back to the counter

  • The cashier hands the order to the customer.

A sequence diagram example for this scenario will have the customer, the cashier, and the kitchen as the three lifelines. They deliver messages back and forth. 

The actions that take place during this sequence are the messages. Such as "Place an order," "Order confirmation," "Order details for preparation," and "Order delivery."

Sequence Diagram Template FAQs

What is the difference between an activity diagram and a sequence diagram?

While both sequence and activity diagrams are UML diagrams, they serve different purposes. A sequence depicts the order in which two or more elements within a system interact, while an activity diagram is a flowchart that illustrates the flow of execution from one activity to another.

How can I make a sequence diagram online?

You can use dynamic platforms like Miro to create a sequence diagram online within minutes. All you have to do is select the Sequence Diagram Template and customize its elements as needed.

What are the basic elements of a sequence diagram?

The most crucial elements of a sequence diagram are lifelines, messages, actors, and activations. There are more complex elements that can help depict complicated or recurring systems.

What does a sequence diagram show?

A sequence diagram shows how two or more elements within a system interact in the sequential order of their interaction. It is a UML diagram that highlights the sequence of messages passed between objects within an application.

UML Sequence Diagram Template

Get started with this template right now.

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