Objectoriented concepts

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Object-oriented concepts UML 2

• LectureAdopting the O-O ParadigmIdentifying
  O-O Entities

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The Object-Oriented Approach

• Adopting the Object Paradigm

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Key Players

• Grady Booch (Booch Method, UML)
• Bjarne Stroustrup (C)
• Coad and Yourdon (OOA, OOD)
• Rumbaugh , Blaha, Premerlani, Eddy and Lorensen
  (OMT, UML)
• Jacobson, Christerson, Jonsson and Overgaard
  (OOSE, UML)
• Wasserman, Pircher and Muller (OOSD)
• NASA (GOOD)
• European Space Agency (HOOD)
• Jackson (JSD, OOJSD)
• Wilfs-Brock (CRC)
• Martin and Odell (Ptech)
• Shlaer and Mellor (OOSA, OODLE)
• Embley (OSA)
• Coleman and Hayes (Fusion)
• Etc. etc. etc. etc .

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Categories of Analysis and Design

• Structured Analysis and Design (eg. SSADM)
• Data-Oriented Analysis and Design (eg. JSP)
• Object-Oriented Analysis and Design (see later)

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The Object Model

• A conceptual framework, a specific way of
  thinking
• Three stages in using O-O to model the
  world-OOA (Object-Oriented Analysis)OOD
  (Object-Oriented Design)OOP (Object-Oriented
  Programming)

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Object-Oriented Analysis

• Examines user requirements
• Produces a model of the problem
• Focus on classes rather than actual object
  instances
• Initial stage prior to design
• Analysis model feeds into design process

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Object-Oriented Design

• Provides solutions to the problem modelled during
  analysis
• Follows on from the analysis process and feeds
  into the implementation stage
• Uses notations to express the logical and
  physical models of the system
• Concentrates on depicting both static and dynamic
  models

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Object-Oriented Programming

• Implements the design models as actual computer
  code
• Utilises some or all of the principles employed
  by object-orientation
• There are many O-O languages, not just Ceg.
  Eiffel, Smalltalk, Object Pascal, Simula
• Some languages are Object-Based rather than
  Object-Oriented, eg. Ada

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Object Model Elements

• Abstraction
• Encapsulation
• Modularity
• Hierarchy
• Typing
• Concurrency
• Persistence

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• Characteristics of Object Orientation
• Data abstraction
• Encapsulation (information hiding)
• Inheritance
• Message passing
• Polymorphism
• Advantages of Object Orientation
• Reusability
• Extensibility
• Modularity
• Intuitiveness

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Abstraction

• Denotes the essential characteristics of an
  object
• Crisply defined conceptual boundaries
• Relative to the perspective of the viewer
• Abstract classes and objects may not actually
  exist

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Encapsulation

• Aka Information hiding
• Abstraction and Encapsulation are complementary
• Compartmentalises the state and behaviour of
  classes and objects that need to be hidden from
  other classes and objects
• Focus on the implementation of non-essential
  characteristics

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Modularity

• Partitioning into individual components to help
  reduce complexity
• Achieved by the use of objects and classes
• We require high cohesion (objects and classes)
  and loose coupling (relationships and message
  passing)

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Hierarchy

• The ranking or ordering of abstractions
• Inheritance is hierarchical
• Subclasses inherit from their superclasses
  (generalisation/specialisation relationship)
• Other relationships can be hierarchical, eg.
  aggregation

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Typing

• Abstract Data Typing (ADT) (eg. char, int,
  float)
• Classes are synonymous to data types
• Both strong and weak typing is possible
• Subclasses related by inheritance from the same
  superclasses are of a similar type. Static
  (early) and dynamic (Late) binding can then
  occur.

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Concurrency

• Multiple events happening at the same time
• Objects are concurrent, they can live and operate
  at the same time (think about it!)
• Objects co-operate and can be both currently
  active or inactive, but still continue to be
  concurrent

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Persistence

• A objects life cycle is dynamic. Instances are
  created, exist for a length of time then are
  destroyed
• However, an object does have the capacity to
  persist, ie. remain in existence across space
  and time
• Thus objects can exist longer than their creator
  and they can move within the address space within
  which they are created

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Digging out Objects, Classes and Attributes

• Look for Nouns, these provide classes, attributes
  and object instances (proper nouns)eg. The cat
  sat on the mat. Cat and Mat are classes A cat
  called Tiddles sat on a mat called
  Martin. Tiddles is an instance of class
  Cat Martin is an instance of class Mat A cat
  with 10 whiskers sat on a mat of length
  2m. Whiskers is an attribute of class Cat and
  has value 10 Length is an attribute of class
  Mat and has value 2m

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Digging out Relationships and Behaviours

• Look for Verbs, these provide insight into the
  relationships between classes/objects and the
  behaviours of classes/objectseg. The cat sat on
  the mat. Class Cat has an association
  relationship with class Mat by sitting on
  it. The cat, which is made up from a cat body,
  cat head, 4 cat limbs and a cat tail, sat on the
  mat. Class cat has a 11 aggregation
  relationship with classes Cat Body, Cat Head,
  Cat Tail and a 14 aggregation relationship
  with class Cat Limbs

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Digging out Relationships and Behaviours

• eg. The purring cat sat on the flying mat. To
  purr is a behaviour of the class Cat To fly is
  a behaviour of the class mat The tiger, which
  is a member of the cat family, sat on the rug,
  which is a kind of mat . Class Tiger inherits
  from the Cat class Class Rug inherits from the
  Mat class

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The UML Method

• Class Diagrams

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Notation Components

• There are two parts to the Class Diagram- 1. A
  graphical Class Diagram 2. Supporting textual
  Specifications
• Both have Essential concepts and Advanced
  concepts

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Graphical Class Diagrams

• Represent the following O-O characteristics using
  various diagrammatical icons-

Parameterised ClassesClass UtilitiesInterfacesA
bstract ClassesConstraintsQualified
Associations Derived Associations Association
Classes
ClassesClass relationships RolesRelationship
NavigabilityVisibilityCompositionNotes
Advanced
Essentials
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The UML Class

• Icon for the Class is-

Appropriate name for the class Name
Class Name Attribute List Operation List
List of class attributes Name Type
List of class methods (behaviours) Name( )
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Class Example

• The Person Class

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Class Relationships

• There are four relationships modelled- Associa
  tions Inheritance Aggregation
  (has) Utilisation (uses)
• Each relationship can be adorned with qualifying
  information (Descriptions, Cardinalities, Roles)

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The Association Relationship

• Has the following icon-

Qualifying Adornment
Role
Role
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Association Example
Host
Attends Birthday Party
Guest
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The Inheritance Relationship

• Has the following icon-

This class ...
inherits ...
from this class
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Inheritance Example
Party Person
DancingStamina Integer
Dance() GiveAPresent()
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The Aggregation Relationship

• Has the following icon-

This class ...
has a number of ...
this class
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Aggregation Example
Party Person
DancingStamina Integer
Dance() GiveAPresent()
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The Utilisation Relationship (via Navigability)

• Introduces the concept of Navigability, ie. one
  class knows about another class directly.
  Utilisation occurs when this knowing about
  involves one class using another.
• Navigability has the icon-

This class ...
knows about ...
this class
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Utilisation Example
Uses
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Cardinality Adornments

• These consist of- 1 Exactly
  one N Unlimited number (ie. zero or
  more) 0 N Zero or more 1 N One or more 0
  1 Zero or one n m Specified range (eg.
  2 8) n m, x Specified range or exact
  number (eg. 2 8, 10)

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Cardinality Example
Class B
Class G
1...N
1
Class A
01
Class C
01
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Class D
Class F
5
Class E
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Visibility Adornments

• Used to indicate the interface of each class.
  Applied to both attributes and methods.
• They consist of- Public access - Private
  access Protected access

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Visibility Example
Uses
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Composition Adornments

• Indicates the method a class uses to contain
  another class. They are indicated on the
  Aggregation Relationship

Simple aggregation (containment by reference)
Composition, ie. Strongly owns its
parts (containment by value)
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Composition Example
Host
Party
- Presents List
0 N
- Start Time Time - End Time Time
- ManageMusic() ReceivePresents() - TidyUp()
Organise() ControlMusic() CleanUp()
Party Person
1 N
- DancingStamina Integer
- Dance() GiveAPresent()
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Use of Notes on Diagrams

• Notes are attached to the various elements of the
  diagram to provide a textual annotation
• Has the following icon-

this element
on ...
Annotation ...
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Example of Using Notes
Host
Party
- Presents List
0 N
- Start Time Time - End Time Time
- ManageMusic() ReceivePresents() - TidyUp()
Organise() ControlMusic() CleanUp()
Party Person
- DancingStamina Integer
1 N
Hopefully, someone will come
- Dance() GiveAPresent()
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Textual Specifications

• Textual specifications are written for the
  following diagram elements- Classes Operati
  ons
• Again, both Essential and Advanced concepts are
  covered

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Class Specifications

• The Class Specification elements we shall be
  concerned with are the following-Responsibiliti
  es A textual description of what the class
  represents and is responsible for in the
  systemAttributes list A list of the
  attributes contained in the classOperations
  list A list of the operations contained in the
  classVisibility How the class, its attributes
  and operations appear to other
  classsesCardinalities How the class scales with
  relation to other classes

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Class Specification Example

• Class CarResponsibilities Represents all
  vehicles which are considered a
  carAttributes Colour Private Engine
  Size Private Registration PrivateOperations
  Move() Public Stop() Public ShowReg() P
  ublic

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Operation Specifications

• The Operation Elements we shall be concerned with
  are the following-Qualification What the
  operation doesReturn class A reference to the
  class the operation returnsArguments List
  of formal argumentsVisibility How the
  operations appear to the other classes,
  therefore indicating the interface to the
  class

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Operation Specification Example

• Operation ShowReg()Qualification Provides an
  inquiring object with the Registration of the
  carReturn Class RegistrationArguments None
  requiredVisibility Public