Should you write a primary scenario for every use case in a use case diagram separately or write one primary scenario that incorporates all the use cases in the diagram?
I'm not sure what your definitions are, but I'm pretty sure the convention is this:
- Use case diagram - a diagram associating actors to use cases.
- Use case - a set of actions, including variants (ie, the primary and alternative paths).
- Scenario - a specific sequence of action (ie, a single path - primary or not).
So by these definitions, you should write a (primary) scenario for each use case.