difference of use case diagram with activity diagram?

Answer 1

A use case describes a sequence of actions that provide the actions that a user does. It is mainly for representing requirements of a new system or a software change. Each usecase has more than one scenario that say how the system should interact with the user or another system to achieve a specificgoal.

The activity diagram is quite different. They usually represent the operational flow of a system. An Activity Diagram shows the overall flow of control of how the system runs.

For instance, a usecase can be like
1 - a user enters his pinnumber
2 - the system grants access

For instance a activity diagram can be like
A diagram representing the flow of data and business logic between tiers databases and information. Can be used in many scenarios.
http://www.tabletuml.com/Help/5%20Activity%20Diagram%20with%20Swimlanes.gif
The example above represents some sort of activity diagram.

Yes, an activity diagram can relate to a usecase diagram in a sence that it starts from an event. An activity diagram needs an event inorder to process it. So in a typical place, a user could be such event.

This is a debatable manner but I hope you can understand the basics.

Answer 2

I know a site that might clear up your confusion. It's called Lucidchart and you can use it to create your own activity diagram. It's really easy to use, I rely on it for all my charts. If you want to learn more about activity diagrams, check it out! www.lucidchart.com/pages/uml/activity-diagram

Answer 3

In high level design document of my project, I have been asked to draw activity diagram for major processes of the system. Now I am confused that whether I have to draw the activity diagram for all the use cases or just for the processes mentioned in Data flow diagram. Please answer if any one can guide me thoroughly on this subject.