OBJECTORIENTED MODELING WITH UML

1
COMP 211INTRODUCTION TOSOFTWARE ENGINEERING

• OBJECT-ORIENTED MODELING WITH UML

2
OBJECT-ORIENTED MODELING WITH UML OUTLINE
2

• Overview of UML
• Modeling and Abstraction
• OO modeling
• aggregation, classification and generalization
• Objects and Classes
• state behaviour
• attributes operations
• Generalization
• inheritance
• coverage
• Links and Associations
• multiplicity
• aggregation composition

3
WHAT IS UML?
2.2

• a general purpose visual modeling language for
  systems
• incorporates current best practice in modeling
  techniques and software engineering
• software development methodology neutral
• industry standard OO modeling language (but can
  also be used for non-OO systems)
• basic premise software systems can be modeled
  as collections of collaborating objects

4
UML STRUCTURE

• Building blocks
• things
• relationships
• diagrams
• Common mechanisms
• specifications
• adornments
• common divisions
• extensibility mechanisms

• Architecture
• use-case view
• logical view
• process view
• implementation view
• deployment view

5
UML STRUCTURE (contd)

• Building blocks - basic UML modeling elements
• things the modeling elements classes,
  interfaces, use case, interactions, packages,
  notes (can be structural, behavioural, grouping
  or annotational)
• relationships specify how two or more things are
  semantically related
• diagrams views into UML models show collections
  of things that visualize what the system will do
  or how it will do it
• Common mechanisms - common ways of achieving
  specific goals
• specifications textual descriptions of the
  semantics of a modeling element
• adornments additional, visual details about
  modeling elements
• common divisions particular ways of thinking
  about the world (e.g., classifier-instance
  interface-implementation)
• extensibility mechanisms ways to customize the
  modeling elements for specific needs

6
UML STRUCTURE (contd)

• Architecture - the strategic aspects of the
  high-level structure of the system that is
  captured in UML by
• use-case view captures the basic requirements
  for the system and provides the basis for the
  construction of the other views
• logical view captures the vocabulary of the
  problem domain as a set of classes and objects
• process view models the executable threads and
  processes in the system
• implementation view models the files and
  components that make up the physical code base of
  the system
• deployment view models the physical deployment
  of components onto computational nodes such as
  computers and peripherals

7
OBJECT-ORIENTED MODELING
2.3

• Why models?

• to abstract reality
• show essential details filter out non-essential
  details
• to help us deal with complexity
• deal with human limitations in understanding
  complex things
• to allow us to focus on the big picture
• to promote understanding of requirements, cleaner
  design, more maintainable systems
• Why objects?
• to more accurately reflect reality in a model
• to reduce the semantic gap between reality and
  a model
• to localize changes to the model
• We can model reality as a number of interacting
  objects

8
OBJECT-ORIENTED MODELING PERSPECTIVES

• conceptual
• do not consider any aspects of implementation of
  objects
• Focus on identifying the objects in the problem
  domain

• specification
• consider interfaces of objects (but no internal
  aspects)
• Focus on how objects interact in the solution
  domain
• implementation
• consider all details of objects (external and
  internal)
• Focus on how to code objects
• Modeling proceeds from the conceptual to
  implementation
• Same OO concepts can be used at all levels to
  build models

9
ABSTRACTION
2.3.2

• mental process of selecting some object
  characteristics and properties to model and
  excluding others that are not relevant

Q
- wings,
landing gear, ...
flies,

• abstraction is always for some purpose
• many different abstractions of the same thing are
  possible
• all abstractions are incomplete descriptions of
  reality
• We do not need completeness, just modeling
  adequacy!

10
QUESTION?
If you had to draw a map of the area around HKUST
to explain to someone how to get to HKUST from
Choi Hung, what is the one most important thing
you would include?

• roads.
• land topology (e.g., contours showing elevation
  above sea level.
• historical sites to see (e.g., the HKUST beach).
• the types and places of vegetation (i.e., trees
  and other types of plants).
• location of hiking trails.
• bus routes.

11
QUESTION?
If you had to draw a map of the area around HKUST
to explain to someone how high the Academic
Building is above sea level, what is the one most
important thing you would include?

• roads.
• land topology (e.g., contours showing elevation
  above sea level.
• historical sites to see (e.g., the HKUST beach).
• the types and places of vegetation (i.e., trees
  and other types of plants).
• location of hiking trails.
• bus routes.

12
TYPES OF ABSTRACTIONS
2.3.2

• classification group similar instances of
  objects

DBMS software
Microsoft software
IS_MEMBER_OF relationship
IS_MEMBER_OF relationship
Sybase
. . .
Access
Oracle
Word
PowerPoint
. . .

• pick out common properties and ignore unique
  properties

13
TYPES OF ABSTRACTIONS (contd)

• aggregation group dissimilar sets of objects

airplane
IS_PART_OF relationship
fuselage
. . .
wing
landing gear

• ignore differences among the parts and
  concentrateon the fact that they form the whole

14
TYPES OF ABSTRACTIONS (contd)

• generalization group similar sets of objects

superclass/supertype
student
IS_A relationship
postgrad
. . .
secondary
undergrad
subclass/subtype

• note difference between classification and
  generalization
• classification applied to individual instances
  of objects
• generalization applied to sets of objects
  (classes)

15
TYPES OF ABSTRACTIONS (contd)

• Note we can combine different types of
  abstraction when modeling

student
generalization
undergrad
classification
John
. . .
Sam
Tina
aggregation
. . .
name
student id
16
QUESTION?

• Consider the relationship between files and
  directories in a computer system. Which type(s)
  of abstraction models this relationship?

• classification only
• aggregation only
• generalization only
• classification and aggregation
• aggregation and generalization
• classification and generalization
• classification, aggregation and generalization
• none of the above

17
OBJECT
2.3.4 2.4.2
a concept, abstraction or thing with crisp
boundaries and meaning which plays a role with
respect to a request for an operation

• interface describes the operationswhich an
  object can perform

18
OBJECT PROPERTIES
Freds Savings Account
identity
19
OBJECT PROPERTIES

• identity unique existence in time and space
• often referenced by a unique identifier, but this
  is not the same as the object
• represented by an object id (OID) for
  implementation purposes
• state static properties of objects that are
  persistent (attributes)
• fixed number of attributes
• either mutable (can be changed) or immutable
  (cannot be changed)
• behaviour dynamic properties of objects that
  describe how objects communicate with each
  other (operations)
• fixed number of operations
• operations invoked by messages received from
  other objects
• message handling may be state dependent
• operations may change an objects state
  (attribute values)
• in many models
• only state or behaviour is emphasized, or
• they are treated separately
• in object-oriented models they are considered
  together since objects contain both aspects

20
OBJECT ENCAPSULATION
a kind of abstraction that enforces a (clean)
separation between the external interface and the
internal implementation of an object
user
request
request
response
response

• hides unnecessary details of implementation
  (information hiding) and ensures modularity
• an object has a visible (public) interface and a
  hidden (private) implementation
• public interface provides services to other
  objects

21
(OBJECT) CLASS
2.3.4 2.4.2

• a description of a group of objects that have
  common
• state relationships
• behaviour semantics

• provides a template to create objects (a
  factory for objects)
• a class is a classifier an object is an instance
• should capture only one abstraction
• one major theme
• should be named using the vocabulary of the
  problem domain
• Most languages allow a class to behave as
  thoughit were an object in its own right

22
WHY CLASSES?
2.3.4 2.4.2

• conveniently describes a collection of objects
  abstraction
• reduces complexity makes systems easier to
  understand
• write-once common definition defined and stored
  once
• specifies what values are acceptable in a given
  context
• allows compilers (and people) to understand the
  programmers intention and to do certain types of
  error checking
• Choosing appropriate classes is animportant
  design decision
• How are classes and modules related?
• classes can be thought of asloosely coupled,
  highly cohesive modules

23
QUESTION?

• Which type of abstraction relates objects and
  classes?
• classification only
• aggregation only
• generalization only
• classification and aggregation
• aggregation and generalization
• classification and generalization
• classification, aggregation and generalization
• none of the above (this is not a type of
  abstraction)

24
CLASS ATTRIBUTE
2.3.4
a description of data values held by objects in a
class

• each attribute has a
• name (unique within a class, but not across
  classes)

• type (specifies the domain of values string,
  integer, money, etc. from which an attribute
  can take its values)
• continuous (e.g., salary) ? discrete (e.g., sex)
• visibility public (), private (-), protected
  (), package ()
• initial value (optional)
• multiplicity (optional number of simultaneous
  values,e.g., telephone number default is
  exactly 1)
• changeability frozen, addOnly, no constraint
  (default)
• base attribute versus derived attribute
• e.g., birthdate versus age

25
ATTRIBUTES UML NOTATION

• stereotype visibility name multiplicity
  typeExpression initialValue propertyString
• propertyString gt a comma separated list of
  properties or constraints
• only name is mandatory
• Examples
• size area (100,000) frozen
• name string
• telephone0..2 string
• telephone1, 3..4 string
• - salary money gt0, lt1,000,000
• You are not required to know this syntax!

26
QUESTION?

• Which type of abstraction relates attributes and
  classes?
• classification only
• aggregation only
• generalization only
• classification and aggregation
• aggregation and generalization
• classification and generalization
• classification, aggregation and generalization
• none of the above (this is not a type of
  abstraction)

27
CLASS OPERATION
2.3.4 2.4.2
a function or transformation that may be applied
to or by objects in a class

• Company hire, fire, pay-dividends,
• Course register, waive-prerequisite,
• invoked by a message sent to an object
• operation signature name of operation (called
  selector), number and types of the arguments, and
  type of the result value
• visibility public (), private (-), protected
  (), package ()
• side effects if the execution of an operation
  changes the state of an object (query operation
  no side effects)

28
OPERATION UML NOTATION

• stereotype visibility name (parameterList)
  returnType propertyString
• parameterList gt kind name typeExpression
  defaultValue
• kind--gt in - pass by value
• out - pass by reference (no input value output
  value only)
• inout - pass by reference (input and output
  value)
• propertyString gt a comma separated list of
  properties or constraints
• isQuery true or false
• isPolymorphic true or false
• concurrency sequential - callers must
  coordinate to ensure only one call to an
  object may execute at one time
• guarded - multiple calls to an object may
  occur simultaneously, but only one is
  allowed to execute at a time other calls are
  blocked
• concurrent - multiple calls may occur
  simultaneously to an object and all execute
  concurrently
• operation signature name (parameterList)
  returnType
• You are not required to know this syntax!

29
CLASS METHOD
2.4.2
the implementation of an operation for a class

• polymorphic operation an operation that can
  have several different methods
• class operation
• Account payInterest
• Savings calculate interest on savings accounts
• Checking calculate interest on checking accounts

• dynamic binding choosing the method to execute
  for an operation based on the objects class

How does a requesting object know whether the
returned value is the result of accessing an
attribute value or of a calculation performed by
a method?
30
SCOPE

• attributes and operations normally have instance
  scope(i.e., they apply to/operate on a single
  object instance)
• sometimes, it is useful to have attributes and
  operations that have class scope (i.e., they
  apply to/operate on an entire class of objects)
• attributes whose values are class determined a
  counter
• object constructors create new object instances
• in UML notation, such attributes/operations are
  underlined

31
CLASS UML GRAPHICAL NOTATION
Visibility public - private protected
package
32
GENERALIZATION
2.4.2

• a relationship between a class and one or more
  refined versions

generalization
Vehicle
vehicle-type
Van
Car
Truck
discriminator
car-size
Compact
Midsize
Fullsize
specialization
discriminator an attribute of enumeration type
that indicates which property of a class is
being abstracted by a generalization
33
GENERALIZATION INHERITANCE
the assumption of properties by a subclass from
its superclasses

• extract similarities (common attributes and
  operations), put them in a superclass and inherit
  them to subclass(es)
• reduces redundancy of descriptions
• promotes reusability of descriptions
• only define properties and behaviour in one
  place
• allows substitution of an object of a
  superclasswith an object of the subclass

34
GENERALIZATION INHERITANCE (contd)

• conflict resolution by
• user-defined order
• predefined order
• redefine names(attributes only)

• subclass may
• add new properties (attributes, operations)

• override methods

Single inheritance
Multiple inheritance
Which withdraw method should CheckingSavings
inherit?
35
MULTIPLE INHERITANCE EXAMPLE
id
id
id
id
id
id
? id
id ?
36
MULTIPLE INHERITANCE EXAMPLE
id
id
id
id
? id
id ?
37
MULTIPLE INHERITANCE EXAMPLE
weight
displacement
name conflict
38
GENERALIZATION ABSTRACT CLASS
a class that has no direct instances

• used for modeling purposes as a container for
  definitions, but no instances of the class are of
  interest

Note Operations may also be abstract ? no
method specified Shown in UML by using italics
39
GENERALIZATION COVERAGE
overlapping - a superclass object can be a member
of more than one subclass
disjoint - a superclass object is a member of at
most one subclass
40
GENERALIZATION COVERAGE (contd)
complete - all superclass objects are also
members of some subclass
incomplete - some superclass object is not a
member of any subclass
41
GENERALIZATION COVERAGE (contd)
overlapping, incomplete
overlapping, complete
42
GENERALIZATION COVERAGE (contd)
disjoint, complete
disjoint, incomplete
43
QUESTION?
What is the policy of the organization?
44
QUESTION?
What is the policy of the organization?
45
LINK
2.4.2
a physical or conceptual relationship between
object instances
Teaches
Works-for

• links allow one object to send messages to
  another object

46
ASSOCIATION
2.4.2

• a description of a group of links with common
  semantics

Teaches
u Teaches
Person
Course

• can show navigability ofassociations(implies
  that the source object has a reference to the
  target object)

class diagram
Works-for

• Works-for

• can show readability ofassociations

• an association is a classifier a link is an
  instance

• conceptually, associations are inherently
  bi-directional

47
ASSOCIATION (contd)

• there can be several associations between the
  same two classes

Attended
Person
University
Works-for
Attended
Works-for

• or even with the same class

Person
Manages
Married-to
48
QUESTION?
Which type of abstraction relates links and
associations?

• classification only
• aggregation only
• generalization only
• classification and aggregation
• aggregation and generalization
• classification and generalization
• classification, aggregation and generalization
• none of the above (this is not a type of
  abstraction)

49
ASSOCIATION DEGREE

• unary (reflexive)
• relates a class to itself

• n-ary - relates any number of classes

• In practice, the vast majority of associations
  are binary

50
ASSOCIATION DEGREE (contd)

• can this be expressed as two binary
  associations?
• suppose we know John has account 532 with HSBC
• John has account 121 with BoC
• Mary has account 993 with BoC

X
?
X
?
v
?
51
ASSOCIATION DEGREE (contd)
532
121
993

• Cannot tell which of Johns accounts is with
  which bank

52
ASSOCIATION DEGREE (contd)
John
121
532
Mary
993

• Cannot tell which BoC account belongs to which
  customer

53
ASSOCIATION DEGREE (contd)
532
121
993
John
Mary

• O.K. Why?

54
ASSOCIATION DEGREE (contd)

• can this be expressed as two binary
  associations?
• suppose we know Mary works on the Accounting
  project using Cobol
• Mary works on the CAD project using C
• John works on the Accounting project using C

X
?
X
?
X
?
55
ASSOCIATION DEGREE (contd)

• Cannot tell that John uses only C on Accounting

56
ASSOCIATION DEGREE (contd)

• Cannot tell which language Mary uses on which
  project

57
ASSOCIATION DEGREE (contd)

• Cannot tell that John works only on Accounting

58
ASSOCIATION DEGREE (contd)
59
ASSOCIATION MULTIPLICITY
2.4.2 5.3.2

• specifies restrictions on the number of objects
  in each class that may be related to objects in
  another class

0..
1..
Instructor
Course
For a given course, how many instructors can
teach it?

• each course must be taught by one instructor but
  may have many

For a given instructor, how many courses can he
teach?

• an instructor does not have to teach any course
  but may teach more than one course in a given
  semester

• a real-world constraint!

60
ASSOCIATION MULTIPLICITY (contd)
A
c..d
a..b
C1
C2
max-card(C1,A)
min-card(C1,A)

• minimal cardinality (min-card)
• min-card(C1,A) minimum number of links in which
  each object of C1 can participate in A

min-card(C1,A) 0 ? optional participation min-ca
rd(C1,A) gt 0 ? mandatory participation

• maximal cardinality (max-card)
• max-card(C1,A) maximum number of links in which
  each object of C1 can participate in A

61
ASSOCIATION MULTIPLICITY (contd)

• special cardinalities

• max-card ? an unlimited upper bound (?)
• min-card 1 and max-card 1 ? can use 1 by
  itself
• min-card 0 and max-card ? can use by
  itself
• max-card(C1,A) 1 and max-card(C2,A) 1
• one-to-one association (11)
• max-card(C1,A) 1 and max-card(C2,A)
• one-to-many association (1N)
• max-card(C1,A) and max-card(C2,A)
• many to many association (NM)

62
ASSOCIATION MULTIPLICITY (contd)

• one-to-one association (11)

0..1
1..1
1
Capital-of
63
ASSOCIATION MULTIPLICITY (contd)
one-to-many association (1N)
1

1..1
0..
Assigned-to
64
ASSOCIATION MULTIPLICITY (contd)
many to many association (NM)


Supplies
65
QUESTION?
?
?
10..45
1..5

• A student must enroll in at least one course and
  can enroll in at most five courses
• A course must have at least ten students enrolled
  in it and cannot have more than forty-five
  students enrolled in it.

66
N-ARY ASSOCIATION MULTIPLICITY

• defined with respect to the other n-1 ends

• given a ternary association among classes (A, B,
  C), the multiplicity of the C end states how many
  C objects may appear in association with a
  particular pair of (A, B) objects

0..1

? 0 or 1 professor

• for each (course, student)

• a student will not take the same course from more
  than one professor, but a student may take more
  than one course from one professor and a
  professor may teach more than one course

• for each (student, professor)

? many courses

• for each (course, professor)

? many students
67
QUESTION?

0..3
0..1
? 0, 1, 2 or 3 days
? 0 or 1 classrooms
? many courses
68
QUESTION?
What is the most likely multiplicity of the
following associations?
69
EXAMPLE

• The classes shown have attributes that are really
  pointers (OIDs) to other classes and which should
  be replaced with relationships. A person may work
  for any number of companies. Each person has an
  ID. A car is assigned an ID. Persons, companies,
  or banks may own cars. Car owner ID is the ID of
  the person, company, or bank who owns the car. A
  car may have only one owner (person, company, or
  bank). A car loan given by a bank may be
  involved in the purchase of a car.
• Prepare a class diagram in which the pointers are
  replaced with relationships. Use associations and
  generalizations as necessary. Show the most
  likely multiplicities for all associations and
  the final attributes for each class.
• Note Your final class diagram should contain no
  IDs.

70
EXAMPLE
71
AGGREGATION/COMPOSITION ASSOCIATION
2.4.2

• a special type of association in which there is a
  part-of relationship between one class and
  another class

Has
Disk
Computer

• a component may exist independent of the
  aggregate object of which it is a part ?
  aggregation

Has
Course-offering
Course

• a component may not exist independent of the
  aggregate object of which it is a part ?
  composition

72
AGGREGATION/COMPOSITION (contd)

• sometimes it is not clear whether the parts
  should be related with           or

Car

• Which aggregation association to use is a matter
  of how one interprets reality and/or the
  requirements of the application

73
WHEN TO USE AGGREGATION/COMPOSITION?

• Would you use the phrase part of to describe
  the association or name it Has? (But be
  CAREFUL! Not all Has associations are
  aggregations.)
• Are operations on the whole automatically applied
  to the part(s) composition?
• Are some attribute values propagated from the
  whole to all or some of the parts?
• Is there an intrinsic asymmetry to the
  association where one object class is subordinate
  to the other(s)?

• It is not wrong to use association rather than
  aggregation! (When in doubt, use association!)

74
ASSOCIATION ROLE NAMES
2.4.2

• role one end of an association

employee
employer

• for binary associations there are two roles

75
ASSOCIATION ROLE NAMES (contd)
role one end of an association
Boss
Person
Manages
Worker
Boss
Worker
Boss

• It is necessary to use role names when an
  associationrelates objects from the same class

76
ASSOCIATION ASSOCIATION CLASS
2.4.2
What about an attribute like grade?
A
B
A-
C
A
B
77
ASSOCIATION ASSOCIATION CLASS (contd)

• Possibility 1 use many attributes for grade

(a) in Student
(b) in Course
78
ASSOCIATION ASSOCIATION CLASS (contd)

• Possibility 2 use a multi-valued attribute for
  grade

(a) in Student
(b) in Course
79
ASSOCIATION ASSOCIATION CLASS (contd)

• Possibility 3 use an association class

80
ASSOCIATION ASSOCIATION CLASS (contd)

• When to associate an attribute with an
  association?

?
salary

• Usually needed only for many to many
  relationships!

81
ASSOCIATION CONSTRAINTS

• ordering

subset
general
82
UML RELATIONSHIPS

• association describes links among object
  instances (only relationship that relates object
  instances)
• generalization relates a more general class
  (superclass) to a more specific kind of the
  general class (subclass)
• dependency relates classes whose behaviour or
  implementation affect other classes
• flow relates two versions of an object at
  successive times
• usage shows that one class requires another class
  for its correct functioning
• realization relates a specification to its
  implementation (e.g., an interface to the
  classes that implement it)

83
STEREOTYPE
a new class of modeling element, which is a
subclass of an existing modeling element

• allows the object model to be dynamically
  extended
• Example we can define different kinds of classes
  that are useful for modeling

boundary OrderForm
entity BankAccount
control PenTracker

• special icons can be used for each stereotype

84
CLASS DIAGRAM EXAMPLE
85
CLASS DIAGRAM EXAMPLE
86
EXAMPLE

• Construct a class diagram for the classes listed
  below. Use association, aggregation and
  generalization relationships as necessary. Show
  multiplicity for all relationships and role names
  where necessary.
• file system drive file directory
• sector ASCII file disk executable file
• track

87
SUMMARY OBJECT-ORIENTED MODELING

• UML Object Model

classifier instance class object attribute
value operation method association link