Looking for feedback on UML diagrams (class & sequence) for university fitness app project <3

[liuheling]

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Hi everyone,

I’m a second-semester Computer Science student working on a Software Engineering assignment at university. The task is to design a simple online fitness/gym application.

As part of the assignment, I need to create:

a UML class diagram
a UML sequence diagram

Since we don’t have exercise sessions and I don’t currently have classmates or instructor feedback available, I’m trying to get some external input to make sure I’m on the right track. At the moment, I’m mainly working with AI tools, but I’m concerned that I might be misunderstanding some concepts without realizing it.

I’m not asking for a full solution or anyone to do the assignment for me — I would really appreciate feedback on whether my diagrams make sense, and especially:

Are there any obvious modeling mistakes?
Is the structure reasonable for a basic software engineering assignment?
Are there any UML conventions I might be violating?

If anyone is willing to take a look, I’d be very grateful. I can share the diagrams here or in a linked image/diagram format.

Thanks a lot for your time!
(I’ve attached the diagrams below.)

dynamic diagram.pdf
ClassDiagram.pdf

[AlpianPPLG]

Hi there! Welcome to the community. It is great to see you taking the initiative to seek external feedback on your Software Engineering assignment. Designing system architecture early on is an excellent habit to build.

Since the community platform doesn't automatically render the contents of your attached dynamic diagram.pdf and ClassDiagram.pdf files directly in the post body, please consider uploading them as image files (PNG/JPG) or pasting your Mermaid.js / PlantUML text code if you used a code-to-diagram tool. That way, everyone can see them instantly!

In the meantime, since you are building an online fitness/gym application, here is a quick checklist of common modeling mistakes and UML conventions that second-semester students frequently encounter. You can cross-reference these with your current drafts:

1. Class Diagram Checkpoints

• Relationship Arrows: Make sure you aren't reversing your arrows. For example, Inheritance/Generalization (a empty, hollow triangle head) should point from the specific class (e.g., PremiumUser) to the base class (User).
• Aggregation vs. Composition: Use aggregation (empty diamond) if a class can exist independently (e.g., a WorkoutRoutine can exist without a specific GymLocation). Use composition (filled black diamond) if the child lifecycle is strictly bound to the parent (e.g., a Gym owns its Rooms; if the gym closes, the rooms cease to exist).
• Multiplicity: Ensure every association line has multiplicity indicators on both ends (e.g., 1 User can have 0..* (zero to many) WorkoutLogs). Leaving these blank is a very common point-deduction on university rubrics.

2. Sequence Diagram Checkpoints

• Lifelines vs. Actors: Ensure your actor (the User/Gym Member) is on the far left, interacting with boundary objects or controllers, not interacting directly with the database or entity classes.
• Return Messages: Remember that return arrows should be dashed lines with an open arrowhead (-->), whereas synchronous call messages must be solid lines with a filled arrowhead (->).
• Focus of Control: Ensure the activation bars (the vertical rectangles on the lifelines) accurately represent exactly when an object is actively processing a method call.

If you can reply with screenshots of your diagrams or paste the underlying structural design descriptions, I would be more than happy to dive deep and give you specific feedback on your application's logic!

[v-coder247]

Hi @liuheling,

Thanks for being a part of the GitHub Community!

If you're looking for help, you might want to try asking for help somewhere that focuses on this specific topic. It's possible that another GitHub user might have run into this same issue and can help, but the GitHub Community Discussions focuses primarily on topics related to GitHub itself or collaboration on project development and ideas. We want to make sure you’re getting the best support you can, but this space may not be the right place for this particular topic.

Best of luck!