For example, I have managers who are responsible for contracts. These contracts belong to a department.So what I have done is this:manager(1) belongs to a department(1)department(1) contains contracts(0..*)In this situation, is it necessary to also include the following relation:manager(1) manipulates contracts(0..*) to find for example who is the manager responsible for this contract?But, I don't need to have this relationship to answer that question. Because I can find it by the first two relationships.So what I wanted to know is if it is necessary to include all relationships in the diagram or if I feel that I don't need this particular relationship I can discard it?
Do I need to include all relationships in my class diagram?
database;database design;relational database;model
First for the general case:A relationship that follows implicitly from other relationships could be left out.In your specific example, this is the case, because there is a one-to-one relationship between manager and department. Therefore if someone is a manager for a department, they (and only they) are the only manager responsible for a contract of that department.If for some reason the relationship between department and manager changes, you will need to re-examine whether you can leave out the relationship between manager and contract.