Domain Model modelling how complex should the diagram be/become?

Question

I am incredibly new to Domain Models and I am trying to build up my understanding. I have created this domain model around a scenario which I will provide. I feel this model is simple and as a result, feels incorrect and might be missing elements I might not have thought of although, I cannot think of what else might need to be included in a domain model given the scenario. The idea is to demonstrate the relationship between real world class entities which I feel I have managed to achieve.

Scenario: Management Application that allows you to create users, projects, companies and issue tickets. The projects are assigned to companies, the users are assigned to projects and the issue tickets are assigned to the users. Tickets have a status which can be changed.

Changes

Implementing proposed changes. I think this is a better way to represent the idea based on the feedback returned, especially in regards to the use of composition. I have also updated the multiplicities to better represent the scenario.

Further changes

Answer 1

The diagram should stay as simple as possible, but not more.

In this specific case:

• The two specializations of User might be too complex for the need: a User stays a User, isn’t it? If you really need to take into account differences between categories of users, and especially if the category changes over time, you'd better consider (object) composition over inheritance (or better worded for UML: prefer association over inheritance).
• The associations might be too simple or incomplete. For example, before an Issue ticket gets assigned to a User, isn’t it also associated to a Project or a Company? It is not clear either if User is also associated to Company (e.g. multi-tenant cloud scenario) or if there is no such association (e.g service provider scenario, where the company is in fact a customer company).
• Some associations may hide association classes, e.g. do you expect to monitor how many time a user worked on a ticket?

Answer 2

It entirely depends on the purpose of your model.

Some models might be created to stimulate discussion and further discovery. Some might be required for the senior stakeholders to approve. Some might be for developers to work from. Others might be for marketing material.

Your model is ok for stimulating discussion and further discovery.