1. Software Architectures
Dr. M.E. Fayad, Professor
Computer Engineering Department, Room #283I
College of Engineering
San José State University
One Washington Square
San José, CA
© M.E. Fayad
SJSU -- CmpE

2. Lesson 4-5: Relationships2
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

3. 3 Lesson Objectives Discuss UML Associations Discuss UML – aggregation
Understand UML- inheritance
Understand How to identify UML
Artifacts 3
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

4. 4 Relationships A relationship is a connection among things
Three most important relationships in OO
dependencies
generalizations
associations
Different kind of lines are used to distinguish various kinds of relationships 4
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

5. 5 Dependencies (1) Dependencies are using relationships
State that a change in specification of one thing (the supplier) may affect another thing that uses it (the client), but not necessary the reverse
Graphically, it is rendered as a dashed directed line 5
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

6. 6 Dependencies (2) Dependent Class Independent Class Client Supplier
Order
Book
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

7. Associations (1)
An association shows a two-way relationship between objects (instances) of two or more classes and requiring special implementation to ensure integrity.
A particular instance of an association is often called a link.
Associations between classes are required if the objects need to communicate.
Associations are often named, and have role-names for each side of the link. 7
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

8. 8 Types of Association Unary association Binary association
both ends of an association circle back to the same class
Binary association
an association that connects exactly two classes
N-ary association
an association that connects more than two classes 8
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

9. Associations (2)
Name
an association can have a name, and the name is used to describe the nature of the relationship
Role
when a class participates in an association, it has a specific role that it plays in that relationship
a role is just the face the class at the near end of the association presents to the class at the other end of the association 9
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

10. 10 Associations (3) Association Name Car Person Vehicle Registration
model
year
# of doors
name
age
address
registeredCar owner
Roles Names 10
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

11. 11 Associations (4) Multiplicity Name Owns by employee employer
1..* *
Person
Company
employee
employer 11
Role Name
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

12. 12 More on Associations Simple example:
An association has a name and a numerical specification (multiplicity indication) of how many objects on one side of the association are connected with how many objects on the other side.
Associations are called use relationships – even if this may seem somewhat cheeky in the example below
displays
0..*
Window
GeomFigure
employs
0..*
Company
Person 12
Employer
Employee
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

13. More on Associations
Associations are directed (one way), bidirectional, and undirected.
UML makes no distinction between bidirectional and undirected associations.
Multiplicity
Stereotype
RelationName
{Constraints} *
Class1
Class2 13
role1
Role2: interface
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

14. More on Associations
Recursive association: A class has a relation with itself.
It is also possible to model associations that are valid only temporarily “stereotype or temporary”
Constraints may be used to restrict the relation under specific aspects.
A role name describes how the object is seen by the opposite object in the association.
An association can be described in more detail by means of constraints, tagged values, and stereotypes.
Stereotypes are noted before or above the relation name, constraints, and tagged values after or below the name. 14
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

15. More on Associations
Directed association is a one-way association, in which one side knows the other, but not vice versa.
Multiplicity Specification:
1 exactly one
0, 1 zero or one
0..4 between zero and four
3, 7 either three or seven 15
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

16. 16 More on Associations More multiplicity specifications:
0..* greater than or equal to zero (default)
* ditto
1..* greater than or equal to one
0..3, 7, 9..* between zero and three, or exactly seven, or greater than or equal to nine. 16
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

17. 17 More Multiplicities Multiplicity
how many objects may be connected across an instance of an association
can be a range of values or an explicit value
exactly one 1
zero or one (optional)
zero or more (many) 0..*
one or more (mandatory) 1..*
numerically specified m..n 17
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

18. More on Associations
Recursive associations are associations in which one class is involved.
has
Patient
Employee
name
staffNo
roomNo
office clerk
relative * * 1
manager
Person
leads 18
reports to
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

19. N-ary Association
An n-ary association is like a common (binary) association, except that more than two association roles involved in it.
N-ary
association
Class1
Class2
Ternary
association 19
Class3
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

20. More on n-ary Association
Reservation
Seat
Train
1..* 1
carriageNo
seatNo
date
trainNo
1..*
Passenger
name
title
Ternary
association 20
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

21. 21 More on Associations N-ary Associations
Recursive Associations
N-ary Associations
Attributed Associations (Association Class)
Association Constraints
Qualified Associations
Derived Associations
Directed Associations
Ordered Associations
Realization/Refinements
Dependency 21
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

22. 22 More on Associations Associations are usually bidirectional
Allows each object involved in the relationship to refer to the object to which it is related.
Bidirectional association means at the relationship has an inverse.
Associations do not have to be bidirectional. 22
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

23. 23 Association Type One-to-One One-to-Many (One-to-Zero-or-More)
Marriage
Woman
Association Type
One-to-One
One-to-Many
(One-to-Zero-or-More)
Many-to-Many
Zero or One
husband wife
Screen
Windows
Window
Nets
Authorization
User
Car
Trailer 23
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

24. 24 Association Type Specified the # of instances on the “many” side
Specify the possible # of
instances using “or”
Ternary relationship
Square
Sides
Line
Secure Room
Occupants
Person
TraditionalFamily
Male
Female
father mother
children 24
Child
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

25. 25 Association Class Connection Connection
Server
Connection
Client
Connection
baudRate
protocol
wireType
disconnect
rerouteLink
• These attributes don’t belong
in either the Client or Server
class.
• They are attributes of the
connection itself. 25
• The association class can have behaviors as well as attributes.
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

26. Aggregation & Composite
Aggregation is a special form of association.
Aggregation is used when the relationship is “part/whole” or “contains/is-part-of”
Aggregation is transitive and operations on “whole” often cascade down to “parts”. 26
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

27. Aggregation & Composite
Computer
Server
Aggregation
“whole”
“part” 52 *
Client
CPU
Disk Drive
Keyboard
Mouse 27
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

28. Aggregation & Composite
Special diamond symbol used on “whole” side to indicate aggregation.
Aggregation is an anti-symmetric that is, if A is part of B, then B is not part of A.
DO NOT confuse aggregation with generalization
An essential property of aggregates is that the whole acts as a proxy for its parts.
A composition is a strict form of aggregation, in which the parts are existence-dependent on the entirely 28
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

29. 29 Aggregation Whole Anywhere from four to many Part Car Body Motor1 1 1 1 1
4..*
Body
Motor
Wheel 29
Part
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

30. Aggregation & Composite
Part
Entirely
Composition
Existence-
DependentPart 30
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

31. Aggregation Problem
Mr. Clinton’s hand is part-of Mr. Clinton & Mr. Clinton is part-of U.S.A.
Therefore:
Mr. Clinton’s hand is part-of U.S.A. 31
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

32. 32 Cash Register Example Keypad * Number Keys Total Key Subtotal Key
display
display
display
drawer
Display
Drawer 32
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

33. Attributes
Attributes are simply the information associated with the object.
The data type used to hold the attributes is often a fundamental type, such as int or char.
Sometimes the attribute can be a non-fundamental type, such as String type and Address type.
Avoid using attributes which might be better implemented as an association to a new class. 33
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

34. 34 More on Attributes * For example: x Using Association
Using Attributes
Using Association TV TV
Manufacturer
String model
String serialNum
String manName
String model
String serialNum
product manu-
facturer
String name
Address address *
Why? Using an association to a Manufacturer class, the name and address of each manufacturer will be stored in one place rather than in each of the TV objects made by that manufacturer. 34
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

35. 35 More on Attributes Employee Employee Split into two classes
If attributes only make sense in some instances of a given class but not in others. It will make sense to split the single class into two classes or more.
Employee
String name
float salary
Employee
Split into two
classes
String name
float salary
long clearanceNum
inheritance
ClearedEmployee 35
long clearanceNum
openVault()
• Not all employees have clearances
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

36. Generalization (1)
A relationship between a general thing (called the superclass or parent) and a more specific kind of that thing (called the subclass or child)
also known as the “is-a-kind-of” relationship
A child
is substitutable for the parent
inherits the properties of its parents 36
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

37. 37 Generalization (2) A class Inheritance
may have zero, one, or more parents
that has no parents and has one or more children is called a root class or a base class
that has no children is called a leaf class
Inheritance
a class with exactly one parent uses single inheritance
a class with more than one parent uses multiple inheritance
Graphically, it is rendered as a solid directed line with a large open arrowhead, pointing to the parent 37
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

38. Inheritance
When a relationship exists between classes such that lower-level classes (called subclasses) share certain attributes and behaviors which can be defined once in a higher-level class (called superclasses).
Subclasses inherit properties (attributes and behaviors) of its superclass and then adds its own unique properties and modifies any inherited properties.
This is called Generalization or Inheritance. 38
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

39. 39 Base and Leaf Classes Base Class Leaf Class Account Bank book
Checking
Loan
Leaf Class 39
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

40. 40 More on Inheritance Window paintWindow size bitmaps icon textWindow
contents 40
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

41. Single and Multiple Inheritance
Account
Loan
Checking
Bank book
Service
Passenger Car
Private Car
Taxi
Single
inheritance
Multiple
inheritance 41
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

42. Aggregation vs. Inheritance
Aggregation Inheritance
Instances of distinct classes Instances of a single class
“a-part-of” (APO) “a-kind-of” or “is-a” (AKO)
Contains superclass-of
Aggregate + parts Superclass + subclass
“and” relationship “or” relationship
Propagated only if specified Inheritance 42
© M.E. Fayad
SJSU -- CmpE M.E. Fayad

43. Discussion Questions
What are the other terms for attributes & operations?
Define an object and a class in UML
What is an association? Give examples
Associations are usually bidirectional. Please describe.
Describe the basic difference between aggregation and inheritance. What do they have in common?
What do you think “multiple inheritance” means?
Which type of association is more likely to yield savings in the amount of code required for implementation? why?
Define the process of identifying objects, classes, inheritance, associations & aggregation, attributes, and behaviors
Define Polymorphism with examples
What do we mean by saying “Model/View/Controller”? 43
© M.E. Fayad
SJSU -- CmpE M.E. Fayad