Lesson 9

Use Case Model Conclusion

User Requirements Use Cases

This module discussed the purpose and scope, elements of, and notation used with the use case model.

The purpose and scope of the use case model: to model the user expectations for the system
The elements of a use case model: the use case diagram and use case narratives
The notation of the use case diagram: the system, actors, use cases, and associations
How to construct a use case diagram from a problem statement
How to document a use case using a narrative of the dialog between an actor and a use case
How to refine the use case diagram using UML extensions called stereotypes
How to use the Includes stereotype (<<includes>>)
How to use the Extends stereotype and generalization (<<extends>>).

Question: What is the purpose and scope of the use case model?
The use case model is a key component of the Unified Modeling Language (UML) and is used to describe the functional requirements of a system from the perspective of its users. The purpose of the use case model is to define the system's behavior in terms of the interactions between the users (actors) and the system. It provides a clear, concise, and comprehensive description of the system's functionality, as well as its intended behavior and usage. The use case model typically includes the following elements:

Actors: These are the users or external systems that interact with the system being modeled.
Use cases: These are the specific functions or features of the system that are of interest to the users. Each use case describes a specific scenario in which the user interacts with the system to achieve a particular goal.
Relationships: These define how the actors and use cases are related. Relationships include the "extends" and "includes" stereotypes, which are used to model optional and mandatory functionality, respectively.
System boundaries: These define the scope of the system being modeled, and help to identify the interfaces between the system and its environment.

The use case model is used throughout the software development lifecycle, from requirements gathering and analysis to design, implementation, and testing. It helps to ensure that the system being developed meets the needs of its users, and that its behavior is consistent with their expectations. It also provides a basis for communication and collaboration among stakeholders, including developers, testers, and end-users.

Glossary terms

Actor:A person, system, or device that interacts with a system in a use case diagram.
Association:A relationship between classes that specifies the type of links that may be created between objects of the associated classes.
Assumptions:Behaviors that must be handled by another use case prior to allowing anyone access to the use case in question.
Encapsulation:The ability to provide users with a well-defined interface to a set of functions in a way which hides their internal workings. In object-oriented programming, the technique of keeping together data structures and the methods (procedures) which act on them.
Exceptional flow of events:A condition that changes the normal flow of control in a system.
Main flow of events: The normal flow of control in a system.
Model element:The smallest unit of semantic definition in a model. The same model element may appear in multiple diagrams. For example, an event appears in sequence diagrams, collaboration diagrams and statechart diagrams. In all three contexts it provides the same semantic information.
Pre-condition: A condition that must test true before execution of the owning task.
Post-condition:A condition that must test true at completion of the owning task.
Triggering event:Event that initiates the use case. The event could be a point in time (for example, month's end), a condition in the system (for example, account is overdrawn), or a request by an actor (for example, selecting an option).
Use case:A use case is a goal that a system must achieve to be considered successful.