Use cases are usefull for gathering potential requirements of the system, this are made during talk with the user and understanding what the user wants. They are little scenarios and they tell us how the system interacts with the end user or another systems.
Use cases should have:
- Actors: is the person, organization, or another system that interacts with the system. It can interact with the system as many times as it wants.
- pre-conditions: are the states or in which the system is prior to the events in the use case.
- post-conditions: are the states in which the system is posterior to the evens in the use case.
For example:
Lets say there’s a property is in auction, and people want to bid online for it.
The actor in a use case of this particular system are the bidders, the ones who want the propery. The pre-conditions are that the user must hace an account with the website to start bidding and the post-conditions are that, after his or her bid, the user can win the bidding.
In this simple example the end user (the bidder) is interacting with a web site (the system). And we can see simple requeriments at first glance; the user must log in.
Joachin's Singularity 