What is a use case?
A use case is a description that lays out the interaction between the user and the piece of software in question. A use case details the a specific task that your program should do. Use cases describe the What of your application. A good practice is to write a use case for every software requirement that your software must comply with.
What must a use case have?
First of all, according to the book. A use case must add value to your application. It should define something that is integral to your program. Second of all, the use case should have an external trigger. Something should jump start each use case. Lastly, the use case should have a clear start and an ending. A use case usually comes as a series of sequential steps.
Why are they important?
A use case can reveal holes in your software requirements. Because a use case requires you to be specific and list all the steps needed to accomplish a task; it helps you to notice certain missing requirements. It can also make you found out about things that your customer forgot to tell you.
Scenarios
A complete path through a use case from the first step to the last is called a scenario. A scenario might have multiple paths. However, they all end in the same user goal.
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