Use Cases Defining user requirements in chunks

Introduction Presentation on Use Cases, includes: Presentation on Use Cases, includes: What is a use case What is a use case Why use them? Why use them? Use Case Symbols defined Use Case Symbols defined

What is a Use Case? Best described by defining a scenario: Best described by defining a scenario: A sequence of steps describing just one interaction between a user and a system. A sequence of steps describing just one interaction between a user and a system. Once defined and understood, a Use Case is simply: Once defined and understood, a Use Case is simply: A set of scenarios tied together by a common user goal. A set of scenarios tied together by a common user goal. A Use Case is used to describe a chunk of functionality of a larger system and is initiated by an actor, and may have other participant actors, e.g. being booked for speeding: initiated by a garda (actor 1) and involving details obtained from the errant driver (actor 2). A Use Case is used to describe a chunk of functionality of a larger system and is initiated by an actor, and may have other participant actors, e.g. being booked for speeding: initiated by a garda (actor 1) and involving details obtained from the errant driver (actor 2).

What is a Use Case (contd…) The actor (better termed role) is an external object such as: The actor (better termed role) is an external object such as: A person (usually) A person (usually) Another system (less common). Another system (less common). Use cases are used in Software Engineering to show developers end users what a system does. Use cases are used in Software Engineering to show developers end users what a system does. Avoids use of computer peoples’ technical terms, but may be full of domain-related jargon. Avoids use of computer peoples’ technical terms, but may be full of domain-related jargon.

Why use them? Simple and easy to understand Simple and easy to understand Expressed mainly textually (unlike most models) Expressed mainly textually (unlike most models) Explains clearly how part of a system works or, in the case of a very simple system, how all of it works. Explains clearly how part of a system works or, in the case of a very simple system, how all of it works. Captures who does what with a system and what the end goals of each user of each part of the system are. Captures who does what with a system and what the end goals of each user of each part of the system are.

Use Case Symbols Actor:- The Use Case: Use Case Communication: Include / Extend::- Generalisation::- The above are the 5 commonly used symbols used in a Use Case Diagram.

Example Use Cases Please see the main use case notes. There are quite a few examples of use case diagrams there, and two verbal descriptions of a use case, one short- form (buying a product on-line) and one long- form (using a point of sales terminal).

Conclusion From this presentation you should know now: From this presentation you should know now: What a use case is What a use case is Why use cases are used Why use cases are used How use cases are expressed, How use cases are expressed, Where to find examples of use cases. Where to find examples of use cases.

Thank You Thank you reading this presentation. Based on a PowerPoint presentation produced by Kevin O’Sullivan and modified by Ian Downey.