Use Cases. Your System at a Glance.
What is a use case, what is it used for and what benefits are offered by use case diagrams?
Use case diagrams show visible behavior of a system as well as the scenarios in which the system interacts with persons or neighboring systems.
Actors are persons or systems outside of the system to be described, e.g. users, customers or processes.
A use case is a scenario that describes the interaction of an actor with a system. It is also a description of what can happen during the process of target achievement.
An extend relationship comprises two use cases one of which includes the other.
If a use case extends another use case the stereotype extend
The result of a use case can be either success or failure/error.
What are Use Cases?
Use Cases document the functionality of a planned or existing system using simple models. A use case describes the visible behavior of a system from the user’s point of view. A user may be a person or a neighboring system and is knows as an actor; he or she interacts with the system in order to achieve a specific goal. A single use case gets its name from the goal the actor wants to achieve and is a series of actions performed in a defined order. Use cases are popular because they are relatively easy to set up and because they substantially increase the interaction between the actors and systems. They are often used in product and software development.
What are Use Cases used for?
Products or software are developed to help people perform tasks more efficiently. A user should be able to use the product in order to reach his or her goals. Very often these goals are not defined clearly. This could lead to delays in the development process and to higher costs. This happens when requirements have not been correctly elicited. In these cases changes need to be implemented, development processes need to be changed and resources have to be distributed differently. The later requirements become apparent the more problematic and expensive the development process will become. A use case bundles all the possible scenarios that could occur when attempting to achieve a goal. In that sense a use case result can be a success, but it can also be a failure or abortion.
