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 include relationship comprises two use cases one of which includes the other.
If a use case extends another use case the stereotype extend is used. An extend relationship is expressed by a dashed line with an arrow.
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.
How to Work with Use Cases in Practice.
Read more about requirements modelling mit objectiF RPM oder objectiF RM »
How Do I Create Use Cases?
Two concepts that need to be implemented together form the basis of the use case approach:
Use case specifications contain information about how use cases interact with actors in an environment. The information is created with the help of templates, it is documented in text and should contain data points such as the: name (including identifier), description, participating actors, priority, criminality, responsibility, conditions, status, other use cases, standard and alternative procedures. Even conditions that are not subject to change, not even when an error has occurred, should be described.
Use cases diagrams from UML (Unified Modeling Language) are graphical models that help you visualize the functionality of a system as well as their relationships with its environment. The important model elements include:
- Use case
- Actors (persons and systems)
- System partitions
- Relationships (extend, include and communicate)
Questions That Help You Create Use Cases
Questions for the actor
- Who uses the system?
- Which other systems interact with the system?
- Who or what delivers information to the system?
- Who or what receives information from the system?
- What is the actor’s goal?
- Which “high level” actions do the actors need to carry out in order to achieve their goal?
Questions about the trigger
- Which event will trigger the use case?
- Which actor will initiate the use case?
Questions about frequency
- How often (per minute/hour/day) is the use case carried out?
Questions about pre-conditions
- Which conditions need to be fulfilled for the use case to come into effect?
- What state must the system be in for the use case to be triggered?
Questions about post-conditions
- Which conditions need to be fulfilled for the use case to be concluded?
- What state must the system be in for the use case to be concluded?
Questions about the standard procedure
- How does the actor interact with the system?
- How does the system react (offer options, show information, execute a process)?
- What will the actor do next?
Questions about alternative procedures
- What happens if…?
- Which alternative actions can the actor perform at every step?
Questions about exceptions
- Which errors or disruptions can occur at every step?
- What should happen if the actor aborts the process?
What should the planned system do?
A use case describes the interactions between users and the system that are necessary to achieve user’s goals.
Better Use Case Diagrams – with tool support
Use cases are the best way to get clarity on what a system should be able to perform. By including actors, systems and system partitions you can get a good impression of the system behavior. Diagrams are particularly well suited to gaining an overview of complex systems. Depending on the tools implemented, use case diagrams offer much more, e.g. the possibility to illustrate dependencies and relationships between requirements, test cases, and system. Additionally so-called extent or include relationships between individual use cases can be illustrated, which will the complete function view on your system, forming the ideal foundation for your product development.