Sequence Diagram - UML 2.0 - object oriented (Basic)

Question

I am learning UML and I've focused on a Netflix-like project on which to practice on.

I'm trying to create a simple sequence diagram for 'stream movie' consisting of only the entity classes (so ignoring objects like the user interface, server, and database).

The idea is that members can search the movie catalog, select a movie, the system will then verify whether they have an unlimited or limited membership. If unlimited, they can stream the movie, otherwise, the system must check whether they have reached their limit of 10 movies that month. If they have, then they can not stream the movie and must receive a message stating why, or be asked to upgrade their account, otherwise, they can stream the movie as normal.

This is the class diagram demonstrating the associations so far:

And this is the sequence diagram for 'stream movie' so far, which I need some assistance with:

What is the best way to build that sequence diagram, yet keeping it relatively simple?

Thanks in advance.

Answer 1

I’m not able to give you a “best way” but I can comment on what I see in your attached diagrams. Maybe you can use this to refine questions that are more specific.

Starting at the bottom, your sequence chart is obviously incomplete. My only comment so far on this is that I don’t understand the logic of the flow, being your member calls “search” movie catalogue which in turn immediately calls “select” movie which in turn calls verify membership. These seem like an unlikely sequence of calls. I sort of get what you mean, I think — I suspect you’re missing return messages, and maybe it should be member that selects movie not the catalogue? Also, you have a member object (identifiable by the colon in “:member”) and then classes for movie catalogue etc. which is not really logical except in very specific contexts.

At the top, your class diagram looks much more complete and understandable. I can only really comment here on design choices rather than UML semantics/syntax. I’m happy to answer any specific questions you have on that but as it’s opinion I won’t post thoughts currently.