11

Software EngineeringDr. K. T. Tsang

Lecture 7

Advanced class modelinghttp://www.uic.edu.hk/~kentsang/SWE/SWE.htm

2

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..*]

3

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(-)

4

Scope – example 1

PhoneMessage

maxDurationmaxDaysRetaineddateRecordtimeRecordedprioritymessagehasBeenReceived

PhoneMailbox

maxMsgCountphoneNumberpassWordgreeting

Person

name

owner

owner

source

*

*

*

0..1

1

1

Not a good model

{ordered}

5

Scope – example 2

PhoneMessage

dateRecordtimeRecordedprioritymessagehasBeenReceived

PhoneMailbox

phoneNumberpassWordgreeting

MailCategory

categoryNamemsgMaxDurationmsgDaysRetainedmsgMaxCount

Person

name

*

*

0..1

1owner

source

{ordered}

1

*

owner

*

1

Preferred model

6

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

7

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

*

8

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??

12

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

15

• 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

substanceName

Reification:

Promote attribute to a class

Substance SubstanceName

substanceName* 1..*

alias

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Constraints on objects

Employee

salary

boss0..1

*(salary<boss.salary)

Window

lengthwidth

(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.

Person

birthdate/ 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 8

State modelinghttp://www.uic.edu.hk/~kentsang/SWE/SWE.htm

38

Reading for this lecture

• Chapter 5 Blaha & Rumbaugh