Copyright 2002 Prentice-Hall, Inc.

Chapter 2Object-Oriented Analysis and Design

Modern Systems Analysis and DesignThird Edition

Jeffrey A. Hoffer Joey F. George

Joseph S. Valacich

Chapter 5System Modeling

Sommerville, "software engineering " , 9th Ed., 2011

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Learning Objectives

Key terms Use Case Object Object class State Behavior Operation Encapsulation Constructor Operation Query Operation Update Operation Association Multiplicity

Abstract Class Concrete Class Class-Scope attribute Abstract operation Method Polymorphism Overriding Aggregation Composition Event State transition Sequence diagram

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Learning Objectives Discuss the concepts and principles underlying the

object-oriented approach Describe the activities in the different phases of the

object-oriented development life cycle State the advantages of object-oriented modeling

versus traditional systems development approaches Learn to develop requirements models using use-

case diagrams Learn to use class diagrams to develop object

models of the problem domain Learn to develop dynamic models using state,

interaction and activity diagrams Model real-world applications using UML diagrams

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IntroductionObject-Oriented systems development life cycle

Process of progressively developing representation of a system component (or object) through the phases of analysis, design and implementation

The model is abstract in the early stages As the model evolves, it becomes more

and more detailed

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The Object-Oriented Systems Development Life CycleAnalysis Phase

Model of the real-world application is developed showing its important properties

Model specifies the functional behavior of the system independent of implementation details

Design Phase Analysis model is refined and adapted to the

environment Can be separated into two stages

System design Concerned with overall system architecture

Object design Implementation details are added to system design

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The Object-Oriented Systems Development Life Cycle

Implementation Phase Design is implemented using a

programming language or database management system

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The Object-Oriented Systems Development Life CycleDeliverables and Outcomes

1. The ability to tackle more challenging problem domains

2. Improved communication among users, analysts, designers and programmers

3. Increased consistency among analysis, design and programming activities

4. Explicit representation of commonality among system components

5. Reusability of analysis, design and programming results

6. Increased consistency among the models developed during object-oriented analysis, design, and programming

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System Modeling

System modeling is the process of developing abstract models of a system, with each model presenting a different view or perspective of that system.

System modeling has now come to mean representing a system using some kind of graphical notation, which is now almost always based on notations in the Unified Modeling Language (UML).

System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers. 8

Existing and planned system models

Models of the existing system are used during requirements engineering. They help clarify what the existing system does and can be used as a basis for discussing its strengths and weaknesses. These then lead to requirements for the new system.

Models of the new system are used during requirements engineering to help explain the proposed requirements to other system stakeholders. Engineers use these models to discuss design proposals and to document the system for implementation.

In a model-driven engineering process, it is possible to generate a complete or partial system implementation from

the system model. 9

The Unified Modeling Language (UML)

A notation that allows the modeler to specify, visualize and construct the artifacts of software systems, as well as business modelsTechniques and notations

Activity diagrams Use cases Sequence diagrams Class diagrams State diagrams

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UML diagram typesActivity diagrams, which show the activities involved in a

process or in data processing .Use case diagrams, which show the interactions

between a system and its environment. Sequence diagrams, which show interactions between

actors and the system and between system components.Class diagrams, which show the object classes in the

system and the associations between these classes.State diagrams, which show how the system reacts to

internal and external events.

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Process Modeling:Activity Diagrams

Shows the conditional logic for the sequence of system activities needed to accomplish a business process

Clearly shows parallel and alternative behaviors

Can be used to show the logic of a use case

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Use-Case ModelingApplied to analyze functional requirements of the systemPerformed during the analysis phase to help developers understand functional requirements of the system without regard for implementation detailsUse Case

A complete sequence of related actions initiated by an actor

Actor An external entity that interacts with the system

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Figure 20-2Use-case diagram for a university registration system

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Use-Case ModelingDeveloping Use-Case Diagrams Use cases are always initiated by an actor Use cases represent complete functionality of the

system

Relationships Between Use Cases Use cases may participate in relationships with

other use-cases Two types

Extends Adds new behaviors or actions to a use case

Include One use case references another use case

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Sequence diagrams

Sequence diagrams are part of the UML and are used to model the interactions between the actors and the objects within a system.

A sequence diagram shows the sequence of interactions that take place during a particular use case or use case instance.

The objects and actors involved are listed along the top of the diagram, with a dotted line drawn vertically from these.

Interactions between objects are indicated by annotated arrows.

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Figure 20-24Sequence diagram for a class registration scenario

with prerequisites

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What are Sequence Diagrams?

Sequence Diagrams are interaction diagrams that detail how operations are carried out.

Dynamic interactions between collaborating objects in the system

Represent a scenario in the systemShow a set of collaborating objects, messages

passing between them, and timing.The diagram captures the behavior of a single use

case. It shows objects and the messages that are passed

between these objects for the particular use case.

What do Sequence Diagrams model?

capture the interaction between objects in the context of a collaboration

show object instances that play the roles defined in a collaboration

show the order of the interaction visually by using the vertical axis of the diagram to represent time what messages are sent and when show elements as they interact over time, showing interactions or interaction instances.

do not show the structural relationships between objects

The purpose of Interaction diagrams is to: Model interactions between objects Assist in understanding how a system (a

use case) actually works Verify that a use case description can be

supported by the existing classes Identify responsibilities/operations and

assign them to classes

Participants in a Sequence Diagram

The sequence diagram consists of Active Objects

Messages represented as solid-line arrows (Means by which objects communicate with each other )

Time represented as a vertical progression

Activation The time period during which an object performs an

operation

Analysis Concepts: Dynamic models

Entity Objects Represent the persistent information tracked by the system

(Application domain objects, “Business objects”)

Boundary Objects Represent the interaction between the user and the system

Control Objects: Represent the control tasks performed by the system

<<entity>> Year

<<entity>> Month

<<entity>> Day

<<control>> ChangeDateControl

<<boundary>> LCDDisplayBoundary

<<boundary>> ButtonBoundary

Dynamic ModelingSequence Diagrams

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

Simple Message A message that transfers control from the

sender to the recipient without describing the details of the communication

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Sequence Diagram - Objects

A life line illustrates what is happening to an object in a chronological fashion

:Name

Life line

Activation

Object

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Sequence Diagram – Time & Messages

Messages are used to illustrate communication between different active objects of a sequence diagram.

:Name1 :Name2

Message Two

Actor Message One

A Simple Sequence Diagram

Basic Notation

Example : Online Shopping In order to develop our sequence diagram we will need the use

case text and the specification class diagram:Use Case Text: Buy a Product Online

1. Customer browses through catalog and selects items to buy.2. Customer goes to checkout.3. Customer fills out shipping information.4. System presents full pricing information, including shipping

information.5. Customer fills in credit card information.6. System authorizes purchase.7. System confirms sale immediately.8. System sends confirming email to customer.

Solution

Questions???

Thanks for your Attention!

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