USE CASE MODELSANDEEP KAUR

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INTRODUCTION

• A Use Case Model describes the proposed functionality of a new system.• A Use Case represents a discrete unit of interaction between a user and the

system.• A Use Case describe how a type of user (called an actor) uses a system to

achieve a goal.

THREE KEY THINGS WE NEED TO DESCRIBE A USE CASE:

• The Actor or Actors involved, An actor is a type of user that interacts with the system.

• The system being used.• The functional goal that the actor achieves using the system.

ACTOR SYSTEM GOAL

ACTOR

• User of a software system are represented as actors in a use case diagram.• Actors represent specific users, groups of users, organizational users and

even external software system.

USE CASE

• Actors maintains relationship with use case.• A use case is a description of some software activity that an actor may

initiate.• Represented as:

HOW THE USE CASE MODEL EVOLVES:

• Both the actor and the use case are found by using the requirements of customers and potential users as vital information.

• As they are discovered, the use case and the actors should be briefly described.• Before the use cases are described in detail, the use case model should be

reviewed by the customer to verify that all the use cases and actors are found.• In iterative development environment, you will select a subset of use cases to be

detailed in each time iteration.• After this flow of events of each use case is described in detail.

• There description show how the system interacts with the actors and what the system does in each individual case.

• Finally, the complete use case model is reviewed, and the developers and customers use it to agree on what the system should do.

WHY STRUCTURING THE USE CASE MODEL:

• Easier to understand.• Easier to maintain.• To partition out common behavior described within many use cases

USE CASE RELATIONSHIPS

• Association: Denotes a relationship between an actor and a use case.• Generalization: Denotes inheritance between use case.• Include: Includes the functionality of one use case in another.• Extend: Extends the functionality of one use case to another under certain

conditions.

• Another asset of organizing the use case model for easier understanding is to group the use case into packages.

• The use case model can be organized as a hierarchy of use case packages, with “leaves” that are actors or use cases.

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