11

Software EngineeringDr. K. T. Tsang

Lecture 7Advanced class modeling

http://www.uic.edu.hk/~kentsang/SWE/SWE.htm

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Multiplicity • Multiplicity - a constraint on cardinality of a set• Multiplicity also applies to attributes• Multiplicity for an attribute specifies the number

of possible values for each instantiation of an attribute

Person

name: string [1]birthday: date [1]phoneNumber: string [*]address: string [1..*]

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Scope & visibility of features• Scope – whether a feature applies to an

object (object scope) or an entire class (static, class scope)

• Visibility – public(+), protected(#) or private(-)

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Scope – example 1

PhoneMessage

maxDurationmaxDaysRetaineddateRecordtimeRecordedprioritymessagehasBeenReceived

PhoneMailbox

maxMsgCountphoneNumberpassWordgreeting

Person name

owner

owner

source

*

*

*

0..1

1

1

Not a good model

{ordered}

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Scope – example 2

PhoneMessage

dateRecordtimeRecordedprioritymessagehasBeenReceived

PhoneMailbox

phoneNumberpassWordgreeting

MailCategory

categoryNamemsgMaxDurationmsgDaysRetainedmsgMaxCount

Person name

*

*

0..1

1owner

source

{ordered}

1

*

owner

*

1

Preferred model

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N-ary Associations• Binary Associations – 2 ends• Ternary Associations – 3 ends• N-ary Associations – n ends, avoid them• Most N-ary Associations can be decomposed

into binary associations

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Restating an N-ary Association• Decompose non-atomic ternary into binary associations

Company

name* *Person

name

Purchase

quantitydatecost

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stock

stock Company

name

**

Person

name

Purchase

quantitydatecost

*

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Example - A genuine ternary associationp.65 B&R, Fig.4.6

Language name

**

Project name

Person name

*programmer

An atomic n-ary association is one that cannot be subdivided into binary associations without losing information.

Class diagram

9object diagram

Java:Language name=“Java”

P135:Project name=“P135”

Mary:Person name=“Mary”

C:Language name=“C”

library:Project name=“library”

Example - A genuine ternary association..

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Example 2 - A ternary association

TextBook

Semester

Course

Professor

roomNumber

DeliveredCourse **

* *

*

A class associates with an association?

p.65 B&R, Fig. 4.7

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Semester

Course

Professor

roomNumber

DeliveredCourse **

*

TextBook *

Example 2 – An n-ary association

A better way??

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Promoting an n-ary association to classes

Semester

Course

Professor

roomNumber

DeliveredCourse *

*

*

TextBook *

A regular class

Programming languages cannot express n-ary association, so we must promote them to class.

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Aggregation• Aggregation is a special form of association

in which an aggregate object is made of constituent parts (is a part of).

• An aggregate object is an extended object treated as a unit in many operation.

• Properties of Aggregation – Transitive: if A is part of B and B is part of C,

then A is also part of C– Anti-symmetric: if A is part of B then B is not part

of A

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Aggregation - example

Auto-mobile

Engine Body Wheel Seat 1 1

** *

*

*

*

UML symbol-Hollow diamond

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• There are 2 forms of part-whole relationships in UML.

• The general form is Aggregation.• The more restricted form is Composition:

– a part can belong to at most to one assembly– once assigned, the part has the same lifetime as

the assembly• Deletion of the assembly object triggers the

deletion of all objects in the composition.

Aggregation & Composition

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Composition - example

Company Division Department

Person*

**1

1

1

UML symbol- solid diamond

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Propagation of operations• The automatic application of an operation to

a group of objects when the operation is applied to a starting object.

• Examples – – Moving an aggregate moves its parts– Copying a document copies all its paragraphs

and all the characters in a paragraph

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Paragraph

copy

Document

copy

Character

copy

*1 *1

Propagation of operations

Person 1

*

The copy operation propagates from document to paragraphs to characters, but not in the reverse direction.

owns

copy copy

p.68 B&R, Fig.4.11

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Abstract & concrete classes• An abstract class has no direct instance but its

descendant classes have direct instances.• A concrete class is a class that can have direct

instances (instantiable).• Abstract class can have abstract operation,

designated by italics or the keyword {abstract}.• An abstract operation defines the signature of an

operation for which each concrete subclass may provide its own implementation.

• A concrete class may not contain any abstract operation.

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Abstract operation - example

Employee yearTodateEarnings

computePay

FullTimeEmployee weeklyRate

computePay

PartTimeEmployee hourlyRate

computePay

Note: Avoid concrete super-class

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Multiple inheritance

• Allows a class to have more than one superclass, and inherit features from all parents.

• Some OOP languages does not support multiple inheritance, e.g. Java.

• Multiple inheritance may create ambiguities. Be careful with its usage.

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Multiple inheritance - example

Employee yearTodateEarnings

computePay

FullTimeEmployee weeklyRate

computePay

PartTimeEmployee hourlyRate

computePay

Partner ownership

computePay

FullTimeEmployeePartner

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• An object is an instance of all ancestors of its class.

Multiple classification

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Multiple classification - example

UniversityMemberPerson

Faculty StudentStaff

*1

Instructor

{overlapping}

Overlapping means a person may belong to more than one kind of UniversityMember

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Delegation using composition of parts

Worker Management

Employee

Manager DirectorFullTime PartTime

1

1 1

1

employmentStatus managerialStatus

p.74 B&R, Fig. 4.19

Workaround for Multiple inheritance: recast a super-class with multiple inheritance as a composition in which each part replaces a subclass (generalization).

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Workaround 2 – nested generalization

Employee

FullTime PartTime

FullTimeManager FullTimeWorker PartTimeManager PartTimeWorker

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Metadata• Metadata is data that describes other data.• Example: A class definition is metadata.• Class is meta-object. Class that describes other

class is meta-class.

CarModel

modelNameyearbasePrice

PhysicalCar

serialNumbercoloroptions

Company Person

*

1

*

1manufacturer owner

*1describes

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Reification• Reification is the promotion of something

that is not an object to an object.

Substance

substanceNameReification:

Promote attribute to a class

Substance SubstanceName

substanceName* 1..*

alias

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Constraints on objects

Employee

salary

boss0..1

*(salary<boss.salary)

Windowlengthwidth

(0.8<length/width<1.5)

Job

priority

(priority never increases)

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Constraint on generalization set (subclasses)

• Disjoint – subclasses are mutually exclusive

• Overlapping – an object can belong to more than one subclass

• Complete – the generalization lists all possible subclasses

• Incomplete – the generalization may miss some subclasses

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• Multiplicity for an association restricts the number of objects related to a given object.

• An ordinary association has no presumed order on the objects of the “many” end. The constraint {ordered} indicates that objects of the “many” end have an order that must be preserved.

Constraint on links

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Subset constraint between associations

Person Committee

Member of

Chair of

(subset)* *

*1

The chair of a committee must be a member of the committee.

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Derived data• Classes, attributes and associations may be

derived from others.• The notation for a derived element is a slash (/)

in front of the element name.• The constraint that determines the derivation

should also be shown.

Personbirthdate/ age

{age=currentDate – birthdate}

CurrentDate

Derived attribute

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Derived object & association

Machine Assembly Part*1*1

offset offset

/ Offset

1

1

offset = MachineAssembly.offset XPartAssembly.offset

/ NetOffset

Derived data can complicate implementation. Use them only if they are truly necessary.

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Package• A package is a group of elements (classes,

associations, generalizations and packages of smaller sizes) with a common theme or purpose.

• Packages partition a model, making it easier to understand or manage.

• Large applications may have several tiers of packages.

PackageName

Notation of a package

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Reading for this lecture

• Chapter 4 Blaha & Rumbaugh

3737

Software EngineeringDr. K. T. Tsang

Lecture 8State modeling

http://www.uic.edu.hk/~kentsang/SWE/SWE.htm

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Reading for this lecture

• Chapter 5 Blaha & Rumbaugh