The requirements use case descriptions are not very specific. There are a number of areas where we've identified requirements but not specific functionality. For example, some of the requirements we can derive from the video rental use case could include:
The store maintains an inventory
The inventory must be available for browsing
The store employs an attendant
There is a mechanism by which the attendant can identify a specific customer
The attendant can identify specific videos
There is a security system triggered by videos leaving the store