I was asked to draw a use case diagram for a fuel filling station (five use cases at minimum). The diagram should show all relationships between the use cases.
Does it mean I have to only draw ONE use case diagram, which includes FIVE use cases in the diagram??
Typically, five use cases are totally fine for one diagram. They should easily fit on one chart, also when including their relationships and the actors. Since it is one system that you describe, why split up? When you exceed 10 use cases, consider generalization or splitting them up into >1 diagram.
Rule of thumb: Make it fit printed on an A4 page.
