Difference between Sequence Diagram and Activity Diagram

Both sequence diagrams and activity diagrams are commonly used in software engineering to model the interactions and flows within a system. They are also useful in other fields, such as business process modeling, to model and analyze the flow of activities or interactions within a business process.

Read this article to find out more about sequence diagrams and activity diagrams and how they are different from each other.

What is Sequence Diagram?

A sequence diagram is a diagram in that is used in representing the sequence of messages flowing from one object to another. The main objective of a sequence diagram is to represent how the messages/events are exchanged between objects and in what time−order.

A sequence diagram mainly focuses on representing the interaction between different objects by pictorial representation of the message flow from one object to another object. They help us visualize the interactions between objects or components in a system and to help understand the flow of information and the relationships between the objects or components.

Sequence diagrams are timeordered which means the exact interactions between objects is represented step by step. They are generally used to describe the behavior of objects in a single usecase.

What is Activity Diagram?

An activity diagram is a type of diagram used in modeling the flow of activities within a system. It helps us visualize the flow activities that are performed in the system, the conditions under which they are performed, and the relationships between those activities.

Activity diagrams are used for modeling the workflow of a system or representing the execution of a process. They simply represent the flow of message from one activity to another. Activity diagrams are used for functional modeling because they describe the general sequence of actions for multiple usecases.

Difference between Sequence Diagram and Activity Diagram

The following table highlights the important differences between a Sequence Diagram and an Activity Diagram −

Key	Sequence Diagram	Activity Diagram
Definition	A sequence diagram models the sequence of messages flowing from one object to another. The emphasis is on representing how the messages/events are exchanged between objects and in what timeorder.	An activity diagram is a diagram that models the control flowing from one activity to another implementing the logic behind these activity with the use of conditional structures, loops, concurrency, etc.
Main focus	Sequence diagrams mainly focus on representing the interaction between different objects by pictorial representation of the message flow from one object to another object. Sequence diagrams are timeordered, which means the exact interactions between objects is represented step by step	Activity diagrams focus on representing the work flow of a system by pictorial representation of the message flow from one activity to another.
Type	Sequence diagrams model the sequential logic, ordering of messages with respect to time. So they are categorized as Dynamic modelling diagram.	An activity diagram mainly represents the process flows captured in a system, so it is not classified as Dynamic modelling diagram.
Use Case	Sequence diagrams are used to describe the behavior of several objects in a particular single use case with implementation of all possible logical conditions and flows.	Activity diagrams are used to describe the general sequence of actions for several objects in several use cases.

Conclusion

The most significant difference between the two is that, a sequence diagram is used to show the message flow from one object to another object, whereas an activity diagram is used to show the message flow from one activity to another activity.