granularity of sequence diagram

Question

I am new to UML, and I am self-learning it, so please bear with me. I am trying to model a system where a teacher can develop an assignment paper and use an LLM to generate answers to make a more robust paper. later, the moderator views the assignment paper and sends feedback; accordingly, the teacher will modify the assignment paper.

This is my use case diagram for the scenario,

Now this is my sequence diagram. Since the login is a basic function I omitted it from my sequence diagram, thinking it increases the granularity of the sequence diagram and I have heard from videos put only what is required. Any help, comment is greatly appreciated. Thanks. I am not confident if I need the steps such as :

1)view create assignment(teacher -> system), 
2)display create assignment (system -> teacher) 
3)view suggested feedback(teacher -> system), 
4)display suggested feedback (system -> teacher)

Answer 1

There is no single good/bad answer to this question, as the level of details of the diagram depend on what you want to tell about this interaction.

A sequence diagram represents an interaction scenario. A long scenario gets more difficult to read. And it's difficult to distinguish what will always happen, from optional part. Your case seems for example to combine a basic creation scenario, with a second scenario related to feedback. The recommendation would then be to split these in two distinct sequence diagram.

Also, your diagram is a lot about user interactions. While acceptable and popular, keep in mind that sequence diagram is not the best tool to model UI. A UI designer may come with better solutions, whereas the sequence diagram imposes a very sequential view. So whenenver you have users in the diagram and are at the level of clicking a button, take a deep breath and try to get rid of details by imagining alternative interfaces such as voice control, just to distinguish what you really need and what comes from your own assumptions about the user interface.

Answer 2

Thanks @Christophe I have seperated the sequence diagrams into two. I am posting this so that anyone who is struggling like me will find it useful. Inaddition to Christophe's answer I also utilised the knowledge from these blog posts Sequence Diagrams Web pages in UML sequence diagrams? C# variables in Sequence diagram

so basically, the text input we write as parameters of our functions. And as Christophe says and the other community, try to make the diagram clear and short. Though I am not sure if I can further compress the functions submitAssignment(assignment) and saveAssignment(assignment) into one, but not sure as the teacher doesn't directly interact with database. Thank you community for helping me