Www. CSE323 การวิเคราะห์และออกแบบระบบ (Systems Analysis and Design) CSE323 การวิเคราะห์และออกแบบระบบ

www.themegallery.com

CSE323CSE323 การวเิคราะห์และออกแบบระบบ การวเิคราะห์และออกแบบระบบ ((Systems Analysis and DesignSystems Analysis and Design))

Lecture 9:Lecture 9:System Design and Detail System Design and Detail DesignDesign

www.themegallery.com

© Bennett, McRobb and Farmer 2005 2

System DesignSystem Design

Based on Chapter 13 of Bennett, McRobb and Farmer:

Object Oriented Systems Analysis and Design Using UML, (3rd Edition), McGraw Hill, 2005.

© Bennett, McRobb and Farmer 2005

3

In This Lecture You Will Learn:In This Lecture You Will Learn:

The difference between analysis and design The difference between logical and physical

design The difference between system and detailed

design The characteristics of a good design The need to make trade-offs in design


4

How is Design Different from How is Design Different from Analysis?Analysis?

Design states ‘how the system will be constructed without actually building it’

(Rumbaugh, 1997) Analysis identifies ‘what’ the system must do Design specifies ‘how’ it will do it


5

How is Design DifferentHow is Design Differentfrom Analysis?from Analysis?

The analyst seeks to understand the organization, its requirements and its objectives

The designer seeks to specify a system that will fit the organization, provide its requirements effectively and assist it to meet its objectives


6

How is Design Different from How is Design Different from Analysis?Analysis?

As an example, in the Agate case study: analysis identifies the fact that the Campaign

class has a title attribute design determines how this will be entered

into the system, displayed on screen and stored in a database, together with all the other attributes of Campaign and other classes


7

When Does Analysis StopWhen Does Analysis Stopand Design Start?and Design Start?

In a waterfall life cycle there is a clear transition between the two activities

In an iterative life cycle the analysis of a particular part of the system will precede its design, but analysis and design may be happening in parallel

It is important to distinguish the two activities and the associated mindset

We need to know ‘what’ before we decide ‘how’


8

Traditional DesignTraditional Design

Making a clear transition from analysis to design has advantages project management—is there the right

balance of activities? staff skills—analysis and design may be

carried out by different staff client decisions—the client may want a

specification of the ‘what’ before approving spending on design

choice of development environment—may be delayed until the analysis is complete


9

Design in the Iterative Life Design in the Iterative Life CycleCycle

Advantages of the iterative life cycle include risk mitigation—making it possible to identify

risks earlier and to take action change management—changes to

requirements are expected and properly managed

team learning—all the team can be involved from the start of the project

improved quality—testing begins early and is not done as a ‘big bang’ with no time


10

SeamlessnessSeamlessness

The same model—the class model—is used through the life of the project

During design, additional detail is added to the analysis classes, and extra classes are added to provide the supporting functionality for the user interface and data management

Other diagrams are also elaborated in design activities


11

Logical and Physical DesignLogical and Physical Design

In structured analysis and design a distinction has been made between logical and physical design

Logical design is independent of the implementation language and platform

Physical design is based on the actual implementation platform and the language that will be used


12

Logical and PhysicalLogical and PhysicalDesign ExampleDesign Example

Some design of the user interface classes can be done without knowing whether it is to be implemented in Java, C++ or some other language—types of fields, position in windows

Some design can only be done when the language has been decided upon—the actual classes for the types of fields, the layout managers available to handle window layout


13

Logical and Physical DesignLogical and Physical Design

It is not necessary to separate these into two separate activities

It may be useful if the software is to be implemented on different platforms

Then it will be an advantage to have a platform-independent design that can be tailored to each platform


14

Model Driven ArchitectureModel Driven Architecture

Note the MDA Generate platform-specific models (PSMs)

from platform-independent models (PIMs)This is discussed in more detail in Chapter 12


15

System Design System Design and Detailed Designand Detailed Design

System design deals with the high level architecture of the system structure of sub-systems distribution of sub-systems on processors communication between sub-systems standards for screens, reports, help etc. job design for the people who will use the

system


16

System Design System Design and Detailed Designand Detailed Design

Object-oriented detailed design adds detail to the analysis model types of attributes operation signatures assigning responsibilities as operations additional classes to handle user interface additional classes to handle data management design of reusable components assigning classes to packages


17

Qualities of AnalysisQualities of Analysis

Correct scope—everything in the system is required

Completeness—everything required is in the system and everything is documented in the models

Correct content—accurate description of requirements

Consistency—each element is consistently referred to by the same name


18

Qualities of DesignQualities of Design

Functional—system will perform the functions that it is required to

Efficient—the system performs those functions efficiently in terms of time and resources

Economical—running costs of system will not be unnecessarily high

Reliable—not prone to hardware or software failure, will deliver the functionality when the users want it


19


Secure—protected against errors, attacks and loss of valuable data

Flexible—capable of being adapted to new uses, to run in different countries or to be moved to a different platform

General—general-purpose and portable (mainly applies to utility programs)

Buildable—Design is not too complex for the developers to be able to implement it


20


Manageable—easy to estimate work involved and to check of progress

Maintainable—design makes it possible for the maintenance programmer to understand the designer’s intention

Usable—provides users with a satisfying experience (not a source of dissatisfaction)

Reusable—elements of the system can be reused in other systems


21

Criteria for Good Design: Criteria for Good Design: CouplingCoupling

Coupling describes the degree of interconnectedness between design components reflected by the number of links an object has

and by the degree of interaction the object has with other objects


22

Criteria for Good Design: Criteria for Good Design: CohesionCohesion

Cohesion is a measure of the degree to which an element contributes to a single purpose

The concepts of coupling and cohesion are not mutually exclusive but actually support each other

Coad and Yourdon (1991) suggested several ways in which coupling and cohesion can be applied within an object-oriented approach


23

Interaction CouplingInteraction Coupling

A measure of the number of message types an object sends to other objects and the number of parameters passed with these message types.

Should be kept to a minimum to reduce the possibility of changes rippling through the interfaces and to make reuse easier.


24

Inheritance Inheritance CCouplingoupling

Vehicle

decription serviceDate maximumAltitude takeOffSpeed

checkAltitude() takeOff()

LandVehicle

numberOfAxles registrationDate register()

Inheritance Coupling describes the degree to which a subclass actually needs the features it inherits from its base class.

Poor inheritance Poor inheritance coupling as coupling as unwanted attributes unwanted attributes and operations are and operations are inheritedinherited


25

Operation Cohesion Operation Cohesion

Lecturer

lecturerName lecturerAddress roomNumber roomLength roomWidth calculateRoomSpace()

{return roomLenght* roomWidth;}

Good operation cohesion but poor class cohesion


26

Poor Specialization CohesionPoor Specialization Cohesion

Address

number street town county country postCode

Person

personName age gender

Company

companyName annualIncome annualProfit

Specialization Cohesion addresses the semantic cohesion of inheritance hierarchies


27

Improved StructureImproved Structure

Address

number street town county country postCode

Person

personName age gender

Company

companyName annualIncome annualProfit

lives at is based at

Improved structure using Address class.


28

Liskov Substitution PrincipleLiskov Substitution Principle

Disinheritance Disinheritance of of debit()debit() means that the means that the left-hand left-hand hierarchy is not hierarchy is not Liskov Liskov compliantcompliant


29

Measurable Objectives in Measurable Objectives in DesignDesign

In Chapter 6, non-functional requirements were described

How can we tell whether these have been achieved?

Measurable objectives set clear targets for designers

Objectives should be quantified so that they can be tested


30


To reduce invoice errors by one-third within a year

How would you design for this?


31


To reduce invoice errors by one-third within a year

How would you design for this? sense checks on quantities comparing invoices with previous ones for the

same customer better feedback to the user about the items

ordered


32


To process 50% more orders at peak periods How would you design for this?

design for as many fields as possible to be filled with defaults

design for rapid response from database design system to handle larger number of

simultaneous users


33

Planning for DesignPlanning for Design

Planning for when platform is known Setting standards Allowing time for training Agreeing objectives and planning tests Agree procedures to decide on trade-offs that

significantly affect the system Planning time for different aspects of design


34

Development StandardsDevelopment Standards

HCI guidelines Input/output device guidelines Construction guidelines


35

I/O I/O DDevice evice HHierarchyierarchy

IODevice

handleEvent()

Sensor

handleEvent()

Actuator

handleEvent()

I/O Hierarchy providing consistency for device handling


36

Prioritizing Design Trade-offsPrioritizing Design Trade-offs

Designer is often faced with design objectives that are mutually incompatible.

It is helpful if guidelines are prepared for prioritizing design objectives.

If design choice is unclear users should be consulted.


37

Trade-offs in DesignTrade-offs in Design

Design to meet all these qualities may produce conflicts

Trade-offs have to be applied to resolve these Functionality, reliability and security are likely to

conflict with economy Level of reliability, for example, is constrained by

the budget available for the development of the system


38

Trade-offs in DesignTrade-offs in Design

Design objectives may conflict with constraints imposed by requirements

The requirement that the system can be used in different countries by speakers of different languages will mean that designers have to agree a list of all prompts, labels and messages and refer to these by some system of naming or numbering

This increases flexibility and maintainability but increases the cost of design


39

Design for ImplementationDesign for Implementation

Initialization and implementation issues should be considered.

There may be data transfer and/or data conversion requirements.


40

SummarySummary

In this lecture you have learned about: The difference between analysis and design The difference between logical and physical

design The difference between system and detailed

design The characteristics of a good design The need to make trade-offs in design


41

ReferencesReferences

More detail about design is provided in Chapters 12, 14 to 18

In particular, Chapter 14 covers Class Design(For full bibliographic details, see Bennett, McRobb

and Farmer)


42

ReferencesReferences

Rumbaugh et al (1991) Coad & Yourdon (1991) Yourdon (1994).

(For full bibliographic details, see Bennett, McRobb and Farmer)

05/05/23 43

Next Lecture:Next Lecture:

Detailed DesignDetailed Design

www.themegallery.com 44

Detailed DesignDetailed Design

Based on Chapter 13 of Bennett, McRobb and Farmer:

Object Oriented Systems Analysis and Design Using UML, (3rd Edition), McGraw Hill, 2005.

45

Class Specification and InterfacesClass Specification and Interfaces Section 14.3 – 14.4 (pp. 397 – 403)

Designing AssociationsDesigning Associations Section 14.5 (pp. 404 – 409)

Integrity ConstraintsIntegrity Constraints Section 14.6 (pp. 409 – 412)

Design Hints for JavaDesign Hints for Java

OutlineOutline

46

Class Specification: Class Specification: AttributesAttributes

nnameame :: type-expression type-expression == initial-value initial-value {{property-property-stringstring}} name is the attribute name type-expression is its data type initial-value is the value the attribute is set to when the

object is first created property-string describes a property of the attribute,

such as constant or fixed

47

Class Specification: Class Specification: AttributesAttributes

BankAccount class with attribute types

included

Shows a derived attribute

BankAccount

nextAccountNumber: IntegeraccountNumber: IntegeraccountName: String {not null}balance: Money = 0/availableBalance: MoneyoverdraftLimit: Money

open(accountName: String):Booleanclose(): Booleancredit(amount: Money): Booleandebit(amount: Money): BooleanviewBalance(): MoneygetBalance(): MoneysetBalance(newBalance: Money)getAccountName(): StringsetAccountName(newName: String)

Arrays can be specified, e.g., qualification[0..10]:String

48

Class Specification: Class Specification: OperationsOperations

operation-name operation-name ((parameter-listparameter-list)) :: return-type- return-type-expressionexpression An operation’s signature is determined by the

operation’s name, the number and type of its parameters and the type of the return-value if any

Which operations• Generally don’t show primary operations (constructor,

destructor, get and set operations)• Only show constructors where they have special

significance• Varying levels of detail at different stages in the

development cycle

49

Class Specification: Class Specification: OperationsOperations

BankAccount class with operation

signatures included.

BankAccount

nextAccountNumber: IntegeraccountNumber: IntegeraccountName: String {not null}balance: Money = 0/availableBalance: MoneyoverdraftLimit: Money

open(accountName: String):Booleanclose(): Booleancredit(amount: Money): Booleandebit(amount: Money): BooleanviewBalance(): MoneygetBalance(): MoneysetBalance(newBalance: Money)getAccountName(): StringsetAccountName(newName: String)

50

Visibility symbol

Visibility Meaning

+ Public The feature (an operation or an attribute) is directly accessible by an instance of any class.

- Private The feature may only be used by an instance the class that includes it.

# Protected The feature may be used either by the class that includes it or by a subclass or descendant of that class.

~ Package The feature is directly accessible only by instances of a class in the same package.

VisibilityVisibility

51

BankAccount class with visibility specified

BankAccount

- nextAccountNumber: Integer- accountNumber: Integer- accountName: String {not null}- balance: Money = 0- /availableBalance: Money- overdraftLimit: Money

+ open(accountName: String):Boolean+ close(): Boolean+ credit(amount: Money): Boolean+ debit(amount: Money): Boolean+ viewBalance(): Money# getBalance(): Money- setBalance(newBalance: Money)# getAccountName(): String# setAccountName(newName: String)

VisibilityVisibility

52

InterfacesInterfaces

An interface in UML is a group of externally An interface in UML is a group of externally visible, i.e., public operations. visible, i.e., public operations. On occasions a class (or some other component) may

present more than one external interface to other classes or the same interface may be required from more than one class.

The interface contains no internal structure, it has no attributes, no associations and the implementation of the operations is not defined.

Formally, an interface is equivalent to an abstract class that has no attributes, no associations and only abstract operations.

53


UML supports two notations to show interfacesUML supports two notations to show interfaces The small circle icon showing no detail A stereotyped class icon with a list of the operations

supported The The realizerealize relationship relationship

indicates that the client class supports at least the operations listed in the interface

is represented by the dashed line with a triangular arrowhead

54

- staffNo - staffName - staffStartDate - qualif ication

CreativeStaff

+ calculateBonus() + linkToNote()

- title - type - targetDate - estimatedCost - completionDate

Advert

+ getCost() + setCompleted() + view()

Realize relationships

«interface» Manageable


«interface» Viewable

+ view()

Manageable Viewable

- companyName - companyAddress - companyTelephone - companyFax - companyEmail - contactName - contactTelephone - contactEmail

Client

+ assignStaffContact() + changeStaffContact()

«use» «use»

«realize» «realize»


55

Designing AssociationsDesigning Associations

One-way vs. Two-way Associations One-way vs. Two-way Associations An association that has to support message passing in

both directions is a two-way association A two-way association is indicated with arrowheads at

both ends Minimizing the number of two-way associations keeps

the coupling between objects as low as possible


57

- staffNo - staffName - staffStartDate - qualification

CreativeStaff

+ calculateBonus() + linkToNote()

*

1

1..*

manage campaign

work on campaign

owns*

1

- title - campaignStartDate - campaignFinishDate - estimatedCost - completionDate - datePaid - actualCost

Campaign

+ assignManager() + assignStaff() + checkBudget() + checkStaff() + completed() + getDuration()

+ getTeamMembers() + linkToNote() + listAdverts() + recordPayment()

- title - type - targetDate - estimatedCost - completionDate

Advert

+ getCost() + setCompleted()

+ view()

*

One - way association

Two - way association


58


Collection ClassesCollection Classes Collection classes are used to hold the object identifiers

when message passing is required from one to many along an association

OO languages provide support for these requirements. Frequently the collection class may be implemented as part of the sending class (e.g. Campaign) as some form of list

59

has

1

*

1

- title: String - campaignStartDate: Date - campaignFinishDate: Date - estimatedCost: Money - completionDate: Date - datePaid: Date - actualCost: Money - ownedAdvertCollection: AdvertCollection

Campaign

+ assignManager() + assignStaff() + checkBudget() + checkStaff() + completed() + getDuration() + getTeamMembers() + linkToNote() + listAdverts() + recordPayment() - title : String

- type: String - targetDate: Date - estimatedCost : Money - completionDate : Date

Advert


owns

- ownedAdvert: Advert [*]

AdvertCollection

+ findFirst() + getNext() + addAdvert() + removeAdvert()

1

One-way One-to-Many Association using a Collection Class




62

Integrity ConstraintsIntegrity Constraints

Referential IntegrityReferential Integrity an object identifier in an object must actually refer to an

object that exists Dependency ConstraintsDependency Constraints

attribute dependencies, where one attribute may be calculated from other attributes, must be maintained consistently

dependency constraints may also exist between or among associations

Domain IntegrityDomain Integrity attributes can only hold permissible values

63

Integrity ConstraintsIntegrity Constraints

Is a member of

Employee

chairs

{subset of}

0..1

*

*

*

Committee

memberCollection[*]

committeeChair

assignChair()

Constraints between Associations

64

Class Design Hints for JavaClass Design Hints for Java

Always keep data private Always initialize data Don't use too many basic types in a class Not all fields need individual field accessors and

mutators Use a standard form for class definitions Break up classes with too many responsibilities Make the names of your classes and methods

reflect their responsibilities

--- Core Java

65

Inheritance Design Hints for JavaInheritance Design Hints for Java

Place common operations and fields in the superclass

Don't use protected fields Use inheritance to model the "is–a" relationship Don't use inheritance unless all inherited

methods make sense Don't change the expected behaviour when you

override a method Use polymorphism, not type information Don't overuse reflection

--- Core Java

CSE323 Systems Analysis and Design 2/2549

6605/05/23

Documents

Www. CSE323 การวิเคราะห์และออกแบบระบบ (Systems Analysis and Design) CSE323 การวิเคราะห์และออกแบบระบบ