AppendixObject-Oriented Analysis and Design: Use Cases and Sequence Diagrams

Modern Systems Analysisand Design

Fifth Edition

Jeffrey A. Hoffer Joey F. George

Joseph S. Valacich

© 2008 by Prentice Hall 2Chapter 7 Appendix

Learning Objectives

Explain use cases and use case diagrams and how they can be used to model system functionality.

Discuss process modeling with use cases for electronic commerce application.

Understand how to represent system logic with sequence diagrams.

Use Cases

Use case is a depiction of a system’s behavior or functionality under various conditions as the system responds to requests from users.

Actor is an external entity that interacts with the system.

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Use Cases (Cont.)

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Figure 7-23 A use case diagram for a university registration system.

Use Cases (Cont.)

Most actors represent user roles, but actors can also be external systems.

An actor is a role, not a specific user; one user may play many roles, and an actor may represent many users.

A use case model consists of actors and use cases.

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Use Cases diagrams

Use case diagram: a picture showing system behavior along with the key actors that interact with the system.

Abstract use case is when a use case is initiated by another use case.

A use case represents completely functionality.

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Definitions and Symbols

Use Case

Actor

Boundary

Connection

Include relationship

Extend relationship

<<include>>

<<extend>>

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Definitions and Symbols (Cont.)

Actor is a role, not an individual. Involved with the functioning of the system at

some basic level.Represented by stick figures.

Use case represents a single system function.Represented as an eclipse.

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Definitions and Symbols (Cont.) System boundary includes all the

relevant use cases.A boundary is the dividing line between the

system and its environment.Use cases are within the boundary.Actors are outside of the boundary.Represented as a box.

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Definitions and Symbols (Cont.) Connection is an association between an

actor and a use case.Depicts a usage relationship.Connection does not indicate data flow.Actors are connected to use cases with lines.Use cases are connected to each other with

arrows.

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Definitions and Symbols (Cont.)

Extend relationship is an association between two use cases where one adds new behaviors or actions to the other.Extends a use case by adding new behavior

or actions.Specialized use case extends the general use

case.

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Definitions and Symbols (Cont.)

Include relationship is an association between two use cases where one use case uses the functionality contained in the other. Indicates a use case that is used (invoked) by

another use case.Links to general purpose functions, used by

many other use cases.

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Definitions and Symbols (Cont.)

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Figure 7-24 A use case diagram featuring an include relationship.

Written Use Cases

Document containing detailed specifications for a use case.

Contents can be written as simple text or in a specified format.

Step-by-step description of what must occur in a successful use case.

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Electronic Commerce Application: Process Modeling using Use Cases Model the functionality of Pine Valley

Furniture Webstore Application with a use case diagram.

Six high-level functions identified to be included in the use case diagram.

The functions represent the “work” or “action” parts of the Website.

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Electronic Commerce Application: Process Modeling using Use Cases (Cont.)

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Figure 7-26 WebStore use case diagram

Dynamic Modeling: Sequence Diagrams Sequence diagram: depicts the interactions

among objects during a certain periods of time. May be presented either in a generic form or in

an instance form. Generic form shows all possible sequences of

interactions – sequences corresponding to all the scenarios of a use case.

Instance form shows the sequence for only one scenario.

Dynamic Modeling: Sequence Diagrams (Cont.) Elements of a sequence diagram

Objects: represented by boxes at top of diagram.

Lifeline: the time during which an object exists.

Messages: means by which objects communicate with each other.

Dynamic Modeling: Sequence Diagrams (Cont.) Activation: the time period during which

an object performs an operation. Synchronous message: a type of

message in which the caller has to wait for the receiving object to finish executing the called operation before it can resume execution itself.

Dynamic Modeling: Sequence Diagrams (Cont.) Simple message: a message that transfer

control from the sender to the recipient without describing the details of the communication.

Asynchronous message: a message in which the sender does not have to wait for the recipient to handle the message.

Designing a Use Case with a Sequence Diagram

Figure 8-11 Sequence diagram for a class registration scenario without prerequisites

Summary In this appendix you learned how to: Explain use cases and use case

diagrams. Explain how they can be used to model

system functionality. Discuss process modeling with use cases

for electronic commerce application. Understand how to represent system

logic with sequence diagrams.

Chapter 7 Appendix 22© 2008 by Prentice Hall