Software Engineering
Dr. K. T. Tsang
Lecture 7
Advanced class modeling
http://www.uic.edu.hk/~kentsang/SWE/SWE.htm
1
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..*]
2
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()
3
Scope – example 1
PhoneMessage
maxDuration
maxDaysRetained
dateRecord
timeRecorded
priority
message
hasBeenReceived
*
*
{ordered}
source
0..1
PhoneMailbox
maxMsgCount
1 phoneNumber
owner passWord
greeting
*
owner 1
Person
Not a good model
name
4
Scope – example 2
Preferred model
Person
name
1
categoryName
msgMaxDuration
msgDaysRetained
msgMaxCount
1 owner
PhoneMessage
*
dateRecord
timeRecorded
priority
{ordered}
message
*
hasBeenReceived
*
MailCategory
*
0..1 PhoneMailbox
source phoneNumber
passWord
owner
greeting
1
5
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
6
Restating an N-ary Association
• Decompose non-atomic ternary into binary associations
stock
Person
*
name
Company
* name
*
Purchase
quantity
date
cost
Person
name
1
*
Purchase
quantity
date
cost
*
stock
1
Company
name
7
Example - A genuine ternary association
p.65 B&R, Fig.4.6
An atomic n-ary association is one that cannot be
subdivided into binary associations without losing
information.
Project
name
Language
*
* name
programmer
Person
*
name
Class diagram
8
Example - A genuine ternary association..
P135:Project
Java:Language
name=“P135”
name=“Java”
Mary:Person
name=“Mary”
library:Project
name=“library”
C:Language
name=“C”
object diagram
9
Example 2 - A ternary association
p.65 B&R, Fig. 4.7
Professor
*
Semester
DeliveredCourse
*
roomNumber
*
Course
*
*
TextBook
A class associates with
an association?
10
Example 2 – An n-ary association
Professor
*
DeliveredCourse
*
Semester
roomNumber
*
*
Course
TextBook
A better way??
11
Promoting an n-ary association to classes
Professor
A regular
class
*
Semester
DeliveredCourse
*
roomNumber
*
TextBook
*
Course
Programming languages cannot express n-ary
association, so we must promote them to class.
12
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
13
Aggregation - example
UML symbol-Hollow
diamond
*
1
Engine
Auto-mobile
*
*
1
*
Body
Wheel
*
*
Seat
14
Aggregation & Composition
• 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.
15
Composition - example
UML symbol- solid diamond
1
Company
*
Division
1
*
Department
1
*
Person
16
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
17
Propagation of operations
Document
copy
1
copy
*
Paragraph
copy
1
copy
*
Character
copy
*
owns
1
Person
The copy operation propagates from
document to paragraphs to characters,
but not in the reverse direction.
p.68 B&R,
Fig.4.11
18
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.
19
Abstract operation - example
Employee
yearTodateEarnings
computePay
FullTimeEmployee
PartTimeEmployee
weeklyRate
hourlyRate
computePay
computePay
Note: Avoid concrete super-class
20
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.
21
Multiple inheritance - example
Employee
yearTodateEarnings
computePay
FullTimeEmployee
PartTimeEmployee
Partner
weeklyRate
hourlyRate
ownership
computePay
computePay
computePay
FullTimeEmployeePartner
22
Multiple classification
• An object is an instance of all ancestors of
its class.
23
Multiple classification - example
Person
1
*
UniversityMember
{overlapping}
Staff
Faculty
Student
Instructor
Overlapping means a person may belong to
more than one kind of UniversityMember
24
Delegation using composition of parts
p.74 B&R, Fig. 4.19
1
1
Employee
1
1
Worker
employmentStatus
FullTime
Management
managerialStatus
PartTime
Manager
Director
Workaround for Multiple inheritance: recast a superclass with multiple inheritance as a composition in
which each part replaces a subclass (generalization).
25
Workaround 2 – nested generalization
Employee
FullTime
FullTimeManager
FullTimeWorker
PartTime
PartTimeManager PartTimeWorker
26
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
1
modelName
year
basePrice
*
describes
PhysicalCar
serialNumber
color
options
*
*
1 manufacturer
1
Company
owner
Person
27
Reification
• Reification is the promotion of something
that is not an object to an object.
Substance
substanceName
Reification:
Promote attribute to a class
Substance
*
alias
1..*
SubstanceName
substanceName
28
Constraints on objects
Window
Employee
boss
0..1
length
width
(0.8<length/width<1.5)
salary
*
(salary<boss.salary)
Job
priority
(priority never increases)
29
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
30
Constraint on links
• 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.
31
Subset constraint between
associations
*
Member of
*
(subset)
Person
1
Chair of
Committee
*
The chair of a committee must be a
member of the committee.
32
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
CurrentDate
birthdate
/ age
{age=currentDate – birthdate}
Derived attribute
33
Derived object & association
Machine
1
*
Assembly
1
*
Part
1
/ NetOffset
offset
offset
1
/ Offset
offset = MachineAssembly.offset X
PartAssembly.offset
Derived data can complicate implementation. Use
them only if they are truly necessary.
34
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.
Notation of a package
PackageName
35
Reading for this lecture
• Chapter 4 Blaha & Rumbaugh
36
Software Engineering
Dr. K. T. Tsang
Lecture 8
State modeling
http://www.uic.edu.hk/~kentsang/SWE/SWE.htm
37
Reading for this lecture
• Chapter 5 Blaha & Rumbaugh
38