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Use case development

Enhance the world with the abilities of both humans and machines.

A use case is a set of actions or event steps that describe how a role (known as an actor in the Unified Modeling Language (UML)) interacts with a system to achieve a goal. A human or some external system might be the actor. Use cases are utilised at a higher level in systems engineering than they are in software engineering, and they frequently reflect missions or stakeholder goals. The precise requirements can then be expressed as contractual declarations or in the Systems Modeling Language (SysML).

The word "use case" has two meanings in software and systems engineering:
● A software usage scenario; typically used in the plural to describe circumstances in which a piece of software could be helpful.
● A scenario in which a system receives and reacts to an external request (such as user input).
● General principle

Use cases are a method for collecting, modelling, and defining a system's needs. A use case is a set of actions that the system may do in conjunction with its actors to generate an observable result that helps it achieve its goals. Human users or other systems play a role in the interaction, which is represented by actors.
A use case is named according to the precise user-goal that it represents for its principal actor throughout the requirement analysis. A written explanation or supplementary graphical models that describe the basic sequence of actions and occurrences, as well as variations such as specific circumstances, exceptions, or incorrect situations, are included in the case.

Variations

The method may be used in a variety of ways and with different variations:

● The needs of a system to be created are specified in system use cases.
● They indicate not only the interactions with the actors, but also the entities engaged in the processing in their thorough description. They serve as the foundation for additional analysis models and design efforts.
● Instead of focusing on a software system, business use cases concentrate on a company. In the context of business process reengineering efforts, they are used to describe business models and business process requirements.

Scope
● The topic indicates the system, subsystem, or component responsible for the interactions.
● The objectives can be organised hierarchically, taking into consideration the level of the organisation interested in the goal (e.g., company, department, user), as well as the sub- goals of the user's goal.
● In contrast to typical functional decomposition, goal decomposition is done from the perspective of the users and independent of the system.

Business use case

A business use case describes the more general interaction between a business system and its users/actors to produce business results of value, similar to how a use case describes a series of events and interactions between a user (or other type of Actor) and a system in order to produce a result of value (goal). The main distinction is that in a business use case model, thesystem studied may include humans in addition to technical systems. These "system users" are referred to as "business workers". In a restaurant, for example, it must be decided whether to consider each individual as an actor (thus outside the system) or a commercial worker (inside the system).

In a restaurant, for example, it must be decided whether to consider each individual as an actor (thus outside the system) or a commercial worker (inside the system). If a waiter is considered an actor, like in the following example, the restaurant system does not contain the waiter, and the model exposes the waiter's interaction with the restaurant. Another option is to see the waiter as a member of the restaurant system (a business worker), while the client as an outsider (an actor).

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Visual modelling

Use cases can include both text and, if necessary, illustrations. Use case diagrams, based on Ivar Jacobson's Objectory notation, are used in the Unified Modeling Language to express the connections between use cases and actors. At the system block level, SysML employs thesame syntax. Other behavioural UML diagrams that may be used to illustrate use cases include activity diagrams, sequence diagrams, communication diagrams, and state machine diagrams. A System Sequence Diagram (SSD) is a diagram that depicts the interactions between external actors and the system under design (SuD), often for visualising a specific scenario of a use case.

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