How we can come to know about what diagrams we should use in a respective project?

Question

Myself and my sister are working on BCA final year projects
1) Load Balancing
2) Food Ordering System
I want to know that, ON WHAT BASIS we choose diagrams such as DFDs, Activity diagrams, E-R diagrams, Class diagrams etc

Answer 1

Try to choose only those diagrams, which are useful for you to know what you need to implement. It always helps me to start with UseCase diagrams, because they design what the users need/want to do. Then I define the requirements which result from the UseCases in words. Then I try to design the first version of a class diagram: Every noun might be a class, every adjective an attribute, every verb a method. That must be optimized later on, of course...
If you have different system components (e.g. client server architecture), it might be useful to add a component diagram.
If you have parallel operations, a sequence diagram helps.
If your business logic in some parts of the program is complicated, use a activity diagram for these parts.
But try to use only the diagrams, that help the reader to understand your project. It's not useful to have diagrams for things the reader knows anyway.

Answer 2

Thank you very much for providing me the basic ideas about choosing different diagrams.