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What is a Use Case Diagram in Software Engineering

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What is a Use Case Diagram in Software Engineering?

For working on any software engineering project, it is essential to clarify what is to be done and how it must be done. The use case Diagram in software Engineering is primarily a visual modeling technique that captures functional requirements in software development. 

The use case diagram describes how an individual who essentially uses a procedure or system will achieve its target. While use cases are related to software engineering, they can be used in reference to any process. As an example, imagine you are a cook, and your goal is to prepare a cheese burst pizza. The use case diagram will depict the sequence of written steps about how the cook would prepare the pizza. A use case diagram will help you recognize where errors can occur and strategize to re-design features to fix the errors.

Application of Use case diagrams 

Generally, a use case diagram represents a high-level outline of the connection between use cases, actors, and systems. Use case diagrams need to be built in the early stages of development. Software Engineers often do apply use cases for software designing modeling purposes.

While a use case can be used to dive into a lot of detail about different possibilities, a use-case diagram can also be used for a top-level view of the system as blueprints or high-level proposals. It is advantageous to write use cases with less detail when it does not require minute detailing about all process aspects.

Use case diagrams are suitable for:

  • Representing the goals of system-user interaction

  • Defining and establishing functional requirements in the system

  • Specifying the framework of the system

  • Capturing the necessities of the system

  • Drive implementation & generate test cases

  • Modeling the basics. Workflow of events in a use case

Unified Modeling Language or UML in software engineering is a standard modeling language. A Use Case diagram is a type of behavioral UML diagram for which the standard is managed by the Object Management Group. Unified Modeling Language includes graphic representation techniques to create visual models of software-intensive systems. 

Building Blocks of Use Case Diagrams 

To understand use case diagram in software engineering, it is extremely important first to know and understand the building blocks/components of Use Case Diagrams:

  • Actors: They are the users that interact with the system. An actor could be a person, organization, even an outside system that interacts with the application or system. They are typically external objects that produce or consume the data. An actor plays a crucial role in the business. An actor is similar to the concept of an individual user; however, they can play multiple roles. A name needs to be given to the actor. For Example: While a professor can be an instructor, they could also be a researcher, therefore, playing two roles with two systems.

  • System: This is typically a specific sequence of actions and interactions between actors and the system. A system may also be referred to as a situation. It helps to identify what is external and internal and the responsibilities of the system. 

  • Use Case/Goal: Use case is the communication between the actor and the system. It’s a pattern of the behavior that the system displays.  It represents the primary piece of the functionality in its entirety from start to the end, the result of most use cases. An effective diagram should describe the actions and variations used to reach the goal.

  • Relationship: This is an association between the use case and the actor. There are different types of use case relationships.

Symbols and notation of use case diagrams

Unlike other UML diagrams, the notation for a  use case diagram in software engineering is relatively straightforward and involves much lesser symbols. Below is the list of different types shapes that you need to know about use case diagrams:

  • Use cases: Horizontally oval shapes represent the different uses that a user might have.

  • Actors: Stick figures denote the people who are employing the use cases.

  • Associations: A-line between actors and use cases. For complex diagrams, it is crucial to understand which actors are related to which use cases.

  • System boundary boxes: This is a box that sets a boundary or system scope to use cases. Any use case outside a box would be considered out of the scope of a system. 

  • Packages: It is a UML shape that permits you to put different elements into groups. Similar to component diagrams, these groupings represent file folders. 

Basic Use Case Examples

Use Case Example-1 - Association Link

A Use Case diagram demonstrates a set of use cases for a system, i.e., the actors and the relationship between the actor and use cases.

Use Case Example-2 - Include Relationship

The “Include relationship” adds extra functionality not detailed in the base use case. The <<Include>> relationship includes common behavior from an included use case into a base use case to provide the reuse of common behavior.

Drawing a Use Case Diagram

In order to begin drawing a Use Case Diagram, system functionalities need to be identified. After every single functionality is identified, they are then transformed into the use cases in the use case diagram. Actors that will interact with the system need to be enlisted.

Once both the actors and use cases are enlisted, the relation between the actor and the use case/system is inspected. It identifies the no. of times an actor communicates with the system. An actor can interact multiple times with a use case or system at a particular instance of time.

Let's take an example of a use case diagram portraying an Online Shopping website:

Here, the Web-based Customer actor makes use of an online shopping website to purchase online. The top-level uses are: View Items, Make Purchase, Checkout, Client Register. 

The View Items use case is utilized by the customer who searches and views products. The Client Register use case permits the customer to register himself on the website for availing gift, discount vouchers, coupons, or a possible private sale invitation. It is important to note that the Checkout is an included use case, which is part of Making Purchase, and thus, it is not available by itself separately.

The Bottom Line

To conclude, Use Case Diagrams are an integral part of Software Engineering. Software engineering is an ever-changing profession.  That said, for long-term career stability, you must explore software engineering courses. You should first get certified in computer science or a related area. There are many options to choose from for those interested in a software engineering degree, whether at graduate and undergraduate levels. Check out this PGP in software development from Great Learning to kick-start your career in software engineering and development.

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