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Slide 12.1

The McGraw-Hill Companies, 2002

Object-Oriented andClassical Software

Engineering

Fifth Edition, WCB/McGraw-Hill, 2002

Stephen R. Schachsrs@vuse.vanderbilt.edu

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Slide 12.2

The McGraw-Hill Companies, 2002

CHAPTER 12

OBJECT-ORIENTEDANALYSIS PHASE

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Slide 12.3

The McGraw-Hill Companies, 2002

Overview

q Object-oriented analysis

q Use-case modeling

q Class modeling

q Dynamic modeling

q Testing during the object-oriented analysis phase

q CASE tools for the object-oriented analysis phase

q Air Gourmet case study: Object-oriented analysis

q Challenges of the object-oriented analysis phase

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Slide 12.4

The McGraw-Hill Companies, 2002

Object-Oriented Analysis Phase

q Object-oriented paradigm

Reaction to perceived shortcomings in structured

paradigm

Problem of larger products

Data and action treated as equal partners

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Slide 12.5

The McGraw-Hill Companies, 2002

Object-Oriented Paradigm

q Object consists of

Data (attributes, state variables, instance

variables, fields, data members), and

Actions (methods, member functions)

q

Objects are independent units Conceptual independence

Physical independence

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Slide 12.6

The McGraw-Hill Companies, 2002

Object-Oriented Analysis (contd)

q Semi-formal specification technique

q Multiplicity of different methods

Booch

OMT

Objectory Shlaer-Mellor

Coad-Yourdon

q All essentially equivalent

q Nowadays, we represent OOA using UML

(unified modeling language)

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Slide 12.7

The McGraw-Hill Companies, 2002

The Three Steps of OOA

q 1. Use-case modeling

Determine how the various results are computed by the

product (without regard to sequencing)

Largely action oriented

q

2. Class modeling (object modeling) Determine the classes and their attributes

Purely data-oriented

q 3. Dynamic modeling

Determine the actions performed by or to each class

Purely action-oriented

q

Iterative process

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Slide 12.8

The McGraw-Hill Companies, 2002

Elevator Problem: OOA

q 1. Use-Case Modeling

Use case: Generic description of overall functionality

Scenario: Instance of a use case

q Get comprehensive insight into behavior of

product

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Slide 12.9

The McGraw-Hill Companies, 2002

Normal Scenario

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Slide 12.10

The McGraw-Hill Companies, 2002

Exception Scenario

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Slide 12.11

The McGraw-Hill Companies, 2002

Class Modeling

q Extract classes and their attributes

q Represent them using an entity-relationship

diagram

q Deduce the classes from use cases and their

scenariosq Often there are many scenarios

Possible danger: too many candidate classes

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Slide 12.12

The McGraw-Hill Companies, 2002

Two Approaches to Class Modeling

q Noun extraction

Always works

q CRC classes

Need to have domain expertise

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Slide 12.13

The McGraw-Hill Companies, 2002

Noun Extraction

q Stage 1. Concise Problem Definition

Define product in single sentence Buttons in elevators and on the floors control the motion of

n elevators in a building with m floors.

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Slide 12.14

The McGraw-Hill Companies, 2002

Noun Extraction (contd)

q Stage 2. Informal Strategy

Incorporate constraints, express result in a

single paragraph Buttons in elevators and on the floors control movement of n

elevators in a building with m floors. Buttons illuminate when

pressed to request the elevator to stop at a specific floor;

illumination is canceled when the request has been satisfied.

When an elevator has no requests, it remains at its current floor

with its doors closed.

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Slide 12.15

The McGraw-Hill Companies, 2002

Noun Extraction (contd)

q Stage 3. Formalize the Strategy

Identify nouns in informal strategy. Use nouns ascandidate classes

q Nouns button, elevator, floor, movement, building, illumination,

illumination, door floor, building, doorare outside problem boundary

exclude

movement, illumination, illumination are abstract nouns exclude (may become attributes)

q Candidate classes: Elevatorand Buttonq Subclasses: Elevator ButtonandFloor Button

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Slide 12.16

The McGraw-Hill Companies, 2002

First Iteration of Class Diagram

q Problem

Buttons do not communicate directly with elevators

We need an additional class:Elevator Controller

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Slide 12.17

The McGraw-Hill Companies, 2002

Second Iteration of Class Diagram

q All relationships

are now 1-to-n

Makes design and

implementation

easier

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Slide 12.18

The McGraw-Hill Companies, 2002

CRC Cards

q Used since 1989 for OOAq For each class, fill in card showing

Name of class

Functionality (responsibility)

List of classes it invokes (collaboration)

Now automated (CASE tool component)

q Strength When acted out by team members, powerful

tool for highlighting missing or incorrectitems

q Weakness Domain expertise is needed

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Slide 12.19

The McGraw-Hill Companies, 2002

3. Dynamic Modeling

q Produce UML state

diagram

q State, event, predicate

distributed over state

diagramq UML guards are in

brackets

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Slide 12.20

The McGraw-Hill Companies, 2002

Testing during the OOA Phase

q CRC cards are an excellent testing technique

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Slide 12.21

The McGraw-Hill Companies, 2002

CRC Cards

q Consider responsibility 1. Turn on elevator button

q Totally unacceptable for object-oriented

paradigm

q

Responsibility-driven design ignoredq Information hiding ignored

q Responsibility1. Turn on elevator button

should be1. Send message to Elevator Button to turn itself on

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Slide 12.22

The McGraw-Hill Companies, 2002

CRC Cards (contd)

q A class has been overlooked

Elevator doors have a state that changes duringexecution (class characteristic)

Add class Elevator Doors

Safety considerations

q Reconsider class modelq Then reconsider dynamic model, use-case

model

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Slide 12.23

The McGraw-Hill Companies, 2002

Second Iteration of CRC Card

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Slide 12.24

The McGraw-Hill Companies, 2002

Third Iteration of Class Diagram

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Slide 12.25

The McGraw-Hill Companies, 2002

Second Iteration of Normal Scenario

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Slide 12.26

The McGraw-Hill Companies, 2002

Elevator Problem: OOA (contd)

q All three models are now fineq We should rather say:

All three models are fine for now

q We may need to return to the object-oriented analysis phase during the object-oriented design phase

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Slide 12.27

The McGraw-Hill Companies, 2002

Why Is All This Iteration Needed?

q Perhaps the method is not yet mature?

Waterfall model (explicit feedback loops)

Rapid prototyping model (aim: to reduce iteration)

Incremental model, and

Spiral modelq Latter two explicitly reflect iterative approach

q Iteration is an intrinsic property of all software

production

Especially for medium- and large-scale products

Expect iteration in the object-oriented paradigm

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Slide 12.28

The McGraw-Hill Companies, 2002

CASE tools for OOA phase

q Diagrams play a major roleq Diagrams often change

Need a diagramming tool

Many tools go further

q All modern tools support UML Example

Rose

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Slide 12.29

The McGraw-Hill Companies, 2002

Air Gourmet Case Study: OOA

q

Use-case model for making a reservation

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Slide 12.30

The McGraw-Hill Companies, 2002

Making a Reservation: Extended Scenario

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Slide 12.31

The McGraw-Hill Companies, 2002

Air Gourmet Case Study: OOA

q Use-case for returning and scanning a postcard

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Slide 12.32

The McGraw-Hill Companies, 2002

Postcards: Extended Scenario

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Slide 12.33

The McGraw-Hill Companies, 2002

Air Gourmet Case Study: Class Modeling

q Stage 1. Concise Problem Definition

Define product in single sentence A computerized system is needed to provide information

regarding the efficacy of a special meals program.

( )

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Slide 12.34

The McGraw-Hill Companies, 2002

(contd)

q Stage 2. Informal Strategy

Incorporate constraints, express result in a single

paragraph Reports are to be generated to document the efficacy of the special

meals program. The reports concern meals loaded on flights, flights

boarded by passengers, names and addresses of passengers, meal

quality, and low-sodium meals.

( td)

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Slide 12.35

The McGraw-Hill Companies, 2002

(contd)

q Stage 3. Formalize the Strategy

Identify nouns in informal strategy. Use nouns as

candidate classes

q Nouns report, efficacy, program, percentage, meal, flight, boarding,

passenger, name, address, quality

efficacy, program, percentage, boarding, quality are abstract

nouns exclude (may become attributes)

name, address are attributes ofpassenger

Question: Should meal and flight be classes?

q It is easier to add classes than to remove them

q Candidate classes: Report and Passenger

Fi t It ti f Cl Di )

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Slide 12.36

The McGraw-Hill Companies, 2002

First Iteration of Class Diagram)

q

Problems with this class diagram Data for reports are needed on a per-flight basis

Each report has to access multiple flights

Each flight has multiple passengers

Six reports (not four) are needed

S d It ti f Cl Di ( td)

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Slide 12.37

The McGraw-Hill Companies, 2002

Second Iteration of Class Diagram (contd)

q Cause of our

problems Flight should

have been a

candidate

class

q BUT, we all

have 2020

hindsight

Ai G t C St d D i M d l

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Slide 12.38

The McGraw-Hill Companies, 2002

Air Gourmet Case Study: Dynamic Model

q State diagram

Ch ll f th OOOA Ph

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Slide 12.39Challenges of the OOOA Phase

q Do not class the boundary into object-oriented

designq Do not allocate methods to classes yet