What is the difference between activity diagram and sequence diagram?

The main difference between activity diagram and sequence diagram is that the activity diagram represents the flow of activities one after another in a system while the sequence diagram represents the sequence of messages flowing from one object to another.

UML (Unified Modeling Language) is a standard language for visualizing, building, and documenting software. It allows implementing object-oriented programming concepts to model the system. Also, it is easier to learn and provides a pictorial representation of the software. Also, there are two types of UML diagrams; They are the structural and behavioral diagrams. Structural diagrams represent the static aspects of the system, while behavior diagrams represent the dynamic aspects of the system. Activity and sequence diagrams are two behavior diagrams.

Key Areas Covered

1. What is an Activity Diagram
     – Definition, Functionality
2. What is a Sequence Diagram
     – Definition, Functionality
3. What is the difference between Activity Diagram and Sequence Diagram?
     – Comparison of key differences

Key terms

Activity diagram, sequence diagram, UML

What is an activity diagram

An activity diagram is a behavior diagram that represents the flow of activities from one to another. Activities represent system operations. An example of an activity diagram is the following.

In the diagram above, the starting point is the initial node, while the arrow represents the flow of activities. The diamond symbol represents a condition. If the condition is true, a set of activities will occur. If the condition is false, another set of activities will occur. After activity 5, there is a fork symbol. It is a division of activities. Then the union symbol combines multiple actions (activity 6, 7, 8) into one. Finally, the end symbol indicates the completion of an activity diagram.

What is a sequence diagram

A sequence diagram is a behavior diagram that represents the interaction between objects over a specific period of time. In other words, it represents the sequence of messages that flow from one object to another.

In the sequence diagram above, the arrows represent the request messages. The dashed arrows represent the return messages, while the vertical rectangular boxes indicate the activation times of the objects. The horizontal rectangle with the underlined text denotes the objects. When considering implementation and execution, it is important to discover the interactions between the components using a sequence diagram.

Difference Between Activity Diagram and Sequence Diagram

Definition

An activity diagram is a graphical representation of step-by-step activity and action workflows with support for choice, iteration, and concurrency. On the other hand, a sequence diagram is a UML diagram that represents the interactions of objects arranged in sequence of time. Thus, this is the main difference between activity diagram and sequence diagram.

main focus

The main focus in an activity diagram is the flow of activities, while the main focus in a sequence diagram is the interaction between objects over a specified period of time. Therefore, this is also an important difference between activity diagram and sequence diagram. 

Use

Another difference between activity diagram and sequence diagram is that an activity diagram helps to model the workflow of a system while a sequence diagram helps to visualize the sequence of calls in a system to perform a specific functionality. .

conclusion

Activity and sequence diagrams are both behavior diagrams. The main difference between activity diagram and sequence diagram is that activity diagram represents the flow of activities in a system while sequence diagram represents the sequence of messages flowing from one object to another.

Reference:

1. “Activity diagram.” Wikipedia, Wikimedia Foundation, November 14, 2018, Available here.
2. “Sequence Diagram.” Wikipedia, Wikimedia Foundation, June 1, 2018, Available here.

Courtesy image:

1. “UML Sequence Diagram” (CC BY-SA 3.0) via Commons Wikimedia

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