Oose_week 10 - Grasp Pattern i

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GRASP PatternGRASP Pattern

Object Oriented Software

Engineering



OutlineOutline

Introduction

Creator

Information Expert

GRASP Patterns 2



IntroductionIntroduction

Design process

!at"s GRASP pattern

!at"s responsibi#it$

Responsibi#ities and met!ods

Responsibi#ities and Interaction Diagrams

GRASP Patterns %



Design ProcessDesign Process

After identif$ing $our re&uirements and

creating a domain mode#' t!en add met!ods

to t!e software c#asses' and define t!emessaging between t!e objects to fu#fi## t!e

re&uirements(

GRASP Patterns )



What is Pattern?What is Pattern? * It is common t!at w!en experts wor+s on particu#ar prob#ems' t!e$ need not

rein,ent t!e w!ee# i(e( t!e$ need not find a comp#ete new so#ution t!at is

comp#ete#$ different from existing so#utions( Rat!er t!e$ remember t!e

simi#ar prob#em and it so#ution and reuse t!e core of it for so#,ing new

prob#em( -!e$ t!in+ in terms of .Problem Solution/ pairs( Abstracting

from suc! pairs and c!urning out t!e commona#ities #eads to patterns(

* Eac! pattern is t!ree0part ru#e w!ic! expresses a re#ation between a certain

context' a prob#em and a so#ution(

* Patterns !a,e names and t!e$ faci#itate communication0 common,ocabu#ar$ and understanding0eas$ to remember w!o#e concept in a

nuts!e##

GRASP Patterns 1



GGeneraleneral RResponsibilityesponsibility

AAssignmentssignment SSoftwareoftware PPatternsatterns

Craig arman coined t!ese terms for t!e first time(

Stands for

Genera# R esponsibi#it$ Assignment Software Patterns(-!e mnemonic meaning cou#d be .successfu# OOAD

3Object Oriented Ana#$sis 4 Design5 re&uires grasping

3understanding5/(

GRASP Patterns 6



GRASPGRASP

GRASP Patterns 7



Whats GRASP patternWhats GRASP pattern

-!is approac! to understanding and using

design princip#es is based on patterns of

assigning responsibi#ities(

-!e GRASP patterns are a #earning aid to

!e#p one understand essentia# object design'and app#$ design reasoning in a met!odica#'

rationa#' exp#ainab#e wa$(

GRASP Patterns 8



Whats responsibilityWhats responsibility

Doing9

* Doing somet!ing itse#f' suc! as creating an object or

doing a ca#cu#ation * Initiating action in ot!er objects

* Contro##ing and coordinating acti,ities in ot!er objects(

:nowing9

* :nowing about pri,ate encapsu#ated data

* :nowing about re#ated objects

* :nowing about t!ings it can deri,e or ca#cu#ate

GRASP Patterns ;



Responsibilities and methodsResponsibilities and methods

9Sa#e

9Pa$ment

ma+ePa$mentcreate

ma+ePa$ment imp#ies Sa#e object !as a responsibi#it$ to

create a Pa$ment objectGRASP Patterns <=



Responsibilities andResponsibilities and

Interaction DiagramsInteraction DiagramsInteraction diagrams s!ow c!oices in

assigning responsibi#ities to objects(

GRASP patterns guide c!oices in w!ere to

assign responsibi#ities(

GRASP patterns are a codification of

wide#$ used basic princip#es(

GRASP Patterns <<



GRASP PatternsGRASP Patterns

; GRASP patterns

Creator

Information Expert

ow Coup#ing

Contro##er

>ig! Co!esion

Indirection

Po#$morp!ism

Protected ?ariations

Pure @abrication

GRASP Patterns <2



!reator !reator

Problem:Problem: !o is responsib#e for creating new instances of somec#ass

Solution:Solution: Assign c#ass B t!e responsibi#it$ to create an instance ofc#ass A if one or more of t!e fo##owing is true9

B aggregates A 3simp#e aggregate s!ared attributes5

B contains A 3composition non0s!ared attributes5

B records instances of A objects

B closely uses A objects

B has the initializing data t!at wi## be passed to A

w!en it is created 3t!us B is an Expert wit! respect to

creating A5 If more t!an one option app#ies' prefer a c#ass B w!ic! aggregates orcontains c#ass A(

GRASP Patterns <%



!reator !reator

Consider abo,e examp#e' sa#e wi## contain man$ Sa#esineItem

objects( Creator GRASP pattern suggests Sa#e is one object t!at

cou#d fu#fi## t!is responsibi#it$(GRASP Patterns <)



"#ample for !reator "#ample for !reator

Consider ?ideoStore and ?ideo in t!at store(

?ideoStore !as an aggregation association

wit! ?ideo(

i(e' ?ideoStore is t!e container and t!e ?ideo is t!e

contained object(

So' we can instantiate ,ideo object in ?ideoStorec#ass

GRASP Patterns <1



"#ample of !reator "#ample of !reator

GRASP Patterns <6



Information "#pertInformation "#pert

Problem:!at is a genera# princip#e of assigning responsibi#ities

to objects

* !o s!ou#d be responsib#e for +nowingdoing

* Domain mode# 3domain expert' domain ana#$sis5 to designmode# 3software c#asses5(

Solution:

Assign a responsibi#it$ to t!e information expert

* t!e c#ass t!at !as t!e information necessar$ to fu#fi## t!e

responsibi#it$(

GRASP Patterns <7



Information "#pertInformation "#pert

Question

Do we #oo+ at t!e Domain Fode# or t!e Design Fode# to ana#$e t!e c#asses

t!at !a,e t!e information needed

Domain model illustrates conceptual classes, design model software classesAnswer

<( If t!ere are re#e,ant c#asses in t!e Design Fode#' #oo+ t!ere first(

2( Ot!erwise' #oo+ in t!e Domain Fode#' and attempt to use 3or expand5 its

representations to inspire t!e creation of corresponding design c#asses(



Example on applyingExample on applying

Start b$ c#ear#$ stating t!e responsibi#it$9

.!o s!ou#d be responsib#e for +nowing t!e tota# of a sa#e

App#$ .Information Expert/ pattern

Assume we are just starting design wor+ and t!ere is no or a

minima# Design Fode#' t!erefore

* Searc! t!e Domain Fode# for information experts t!e

rea#0wor#d Sa#e is a good candidate(

-!en' add a software c#ass to t!e Design Fode# simi#ar#$

ca##ed Sale, and give it the responsibility of knowing its tota#'

expressed wit! t!e met!od named getTotal.



"#ample$ What information is"#ample$ What information is

needed to determine the grand total?needed to determine the grand total?

Sa#e

date

Product

description

price

itemID

GRASP Patterns 2=



Sa#e

date

Product

description

price

itemID

Sa#esineItem

&uantit$

!o is information expert

GRASP Patterns 2<

"#ample !ontd"#ample !ontd



Sa#e

date

Product

description

priceitemID

Sa#esineItem

&uantit$

get-ota#

getSub-ota#

getPrice

GRASP Patterns 22

"#ample !ontd"#ample !ontd



"#ample %"#ample %

Assume we need to get a## t!e ,ideos of a ?ideoStore(

Since ?ideoStore +nows about a## t!e ,ideos' we canassign t!is responsibi#it$ of gi,ing a## t!e ,ideos can

be assigned to ?ideoStore c#ass(

?ideoStore is t!e information expert(



"#ample % contd&"#ample % contd&

Oose_week 10 - Grasp Pattern i

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