Use Case Diagram

A use case is a description of a system's function from the user's perspective. Use cases work by describing the typical interaction between a system's user and the system itself through a story of how the system is used. The sequence of steps that explains the interaction between the user and the system is called a scenario. Each scenario describes a sequence of events. Each sequence is initiated by a person, another system, a piece of hardware or a time sequence. In short, a use case can be said to be a set of scenarios tied together by a common user goal.

In discussions about use cases, the user is usually called an actor. An actor is a role that a user can play in their interaction with the system.

The use case model is part of the requirements model (Jacobson et al. 1992). It includes the problem domain object model and a description of the user interface. Use cases specify the functions offered by the system from the user's perspective.

Use Case Description

A use case is an abstraction of the interaction between the system and an actor, so it is very important to choose the right abstraction. For example, when a customer phones a restaurant to make a booking, they will speak to a restaurant employee who will record the booking in the system. To do this, the employee plays the role of a receptionist, even though that may not be their formal job. In this situation, the employee is an instance of the receptionist actor, and the interaction between the employee and the system is an instance of a use case.

Use cases are created based on the needs of the actor. A use case must be 'what' the application software does, not 'how' the application software does it. Each use case must be given a name that states what is achieved as a result of its interaction with the actor. A use case name may consist of several words, and no two use cases may have the same name.

Purpose of a Use Case Diagram

Use case diagrams are used to capture the dynamic aspects of a system. More specifically, use case diagrams are used to gather the requirements of a system, whether from internal or external influences.

Use cases can be used to depict a top-level requirements analysis of the system through the system's functionality and the interactions among the actors. An actor is something that interacts with the system.

• In general, the purposes of a use case diagram can be described as follows:
• Used to gather the requirements of a system
• To get an outside view of the system
• To identify the factors that influence the system, both internal and external
• To show the interactions among the system's actors

Use Cases: Why Do They Matter?

Use cases are the best tool for encouraging potential users to talk about a system from their own point of view. It is not always easy for users to state how they intend to use a system. Because traditional system developers are often careless in doing analysis, users often find it hard to answer when asked for input on something.

The basic idea is to involve system users in the early phases of system analysis and design. That way, it is hoped that a system that actually helps users can be built. Keep in mind that a use case represents the view from outside the system.