Use cases: details

At this point, each use case is detailled by the way of "scenarii", i.e. sequence diagrams between an actor and the system.
In general, there is a nominal scenario ("everything is ok") followed by a lot of secondary scenarii ("everything goes wrong").

Use cases' diagram: details

Thus, scenarii descibe how to realize a functionality (with general then particular cases).

Each scenario is then documented : for instance, a "card" has a number, a name and a crc code, the "code" is obtained by querying the bank of the card, the "amount" must be a sum of 50, 20 and 10 euros, etc.