What's the difference between activity diagram and sequence diagram?

Question

I'm studying UML and I am confused. What's the difference between activity diagram and sequence diagram? I haven't got the crucial point yet.

Answer 1

They are both behavioral diagrams but have different emphases.

• Activity diagram is good at depicting the control flowing from one activity to another, especially good at the logic of conditional structures, loops, concurrency.
• Sequence diagram is good at depicting the sequence of messages flowing from one object to another, how their messages/events are exchanged in what time-order.

Notice that sequence diagram may also express conditions, loops and concurrency by using guards, but they are not as intuitive and convenient as those in activity diagram.

Answer 2

Activity diagrams represents the flow of use cases. But sequence diagrams represents the interaction between classes or objects according to time.So there is a difference between these two diagrams.

Before moving to activity diagrams you need to draw the use case diagram. using use case(system behaviour) diagram you can identify activities(behaviours).

Then you need to draw the the activity diagram to show the flow of behaviours.

then You need to identify the classes and draw the class diagram.

Using class diagram you can draw the sequence diagrams to show the interaction between classes.

1. use case diagram
2. activity diagram
3. class diagram
4. sequence diagram