To me, the biggest differences between a User Story and a Use Case are:
- A user story is a lightweight document that can be written on a card (In order to , as a , I want ). A User Story doesn't capture all the details, it's an informal support for the discussion.
- A use case is an heavyweight document that needs a word document. It describes a "Normal Flow" of steps and/or actions and "Alternative Flows" which are detailed. A Use Case captures all the details, it's a formal specification.
According to Scott W. Ambler on Usage Scenarios, these artifacts look like a Use Case's flow:
A usage scenario, or scenario for short, describes a real-world example of how one or more people or organizations interact with a system. They describe the steps, events, and/or actions which occur during the interaction. Usage scenarios can be very detailed, indicating exactly how someone works with the user interface, or reasonably high-level describing the critical business actions but not the indicating how they’re performed.
Honestly, the differences with a Use Case's flow is not crystal clear, even after reading this paragraph (the last sentence being maybe the most important):
As you can imagine, there are several differences between use cases and scenarios. First, a use case typically refers to generic actors, such as Customer, whereas scenarios typically refer to examples of the actors such as John Smith and Sally Jones. There’s nothing stopping you from writing a generic scenario, but it’s usually better to personalize the scenarios to increase their understandability. Second, usage scenarios describe a single path of logic whereas use cases typically describe several paths (the basic course plus any appropriate alternate paths). Third, in UP-based processes use cases are often retained as official documentation whereas scenarios are often discarded after they’re no longer needed.
I may be wrong, but Usage Scenario really sounds like Use Case flow but rebranded with an Agile touch.