Multimedia

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Multimedia Website Design

• Object Orientation Concepts

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Introducing Object Orientation

• What youll learn in this lecture -
• Why UML is necessary
• How UML came to be
• Diagrams of UML
• Multi-diagram approach to modelling

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What is OO?

• OO is a way of thinking
• Applying real world concepts to the components
  that go together to make software
• The theory rests on software reuse writing a
  piece of software that you can use again
• The UML represents objects

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Why OO?

• Software Reuse use an object again. Share your
  objects with other programmers
• Communication much easier if you can talk in
  real world examples
• Breaks down complex software into manageable
  chunks

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What is an Object?

• An object is an instance of a class
• An object represents a real world item, or a
  component of one
• e.g. A Computer is a class
• e.g. A hard drive is a class that has a
  relationship with the computer class

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What is a class made up of?

• An class contains attributes and operations
• An attribute is a property of the class, which is
  instantiated in the object
• An operation is a function of the class, which
  executes according to the objectsattributes

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Class Task 1

• Read the scenario which proposes swipe cards for
  LSD.
• Working on your own, identify all the important
  nouns in the document which will become classes
  in our design.

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OO Concepts

• OO is a way of thinking about software
  development using concepts
• Abstraction
• Inheritance
• Polymorphism
• Encapsulation
• Message Sending
• Associations
• Aggregation

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Abstraction

• An Abstraction is a representation of an object
  from its real-world counterpart
• Its attributes and operations do not have to
  correspond to the exact item
• e.g. A car object does not need to have a
  startWindowWipers operation if you dont need to
  call it

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Inheritance

• An object inherits all of its classes
  attributes and operations
• However, a class can also inherit from a parent
  class
• e.g. a car class inherits some of its
  operations and attributes from its parent,
  vehicle class
• Therefore, if a car class inherits from a
  vehicle class and so does a motorcycle class,
  car and motorcycle will share the same
  components of vehicle

Vehicle
startEngine()
Car
Motorcycle
startEngine()openBoot()
startEngine()useCentreStand()
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Polymorphism

• Sometimes an operation can have the same name in
  many classes
• e.g. You can turn on a light, a car, a kettle,
  etc
• It is important that the operation being called
  belongs to the class you intended to use
• If a parent class has an operation show then
  its up to the developer to implement the correct
  operation in their class

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Encapsulation

• Encapsulation is hiding away functionality that
  the developer doesnt need to know how it works
  in order to use it
• The Black Box approach
• This way you can build complex applications
  without having to know how it all works!

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Messages

• A Message is a piece of information that is sent
  from one object to another
• i.e. the joypad sends a message to the XBOX and
  the XBOX object responds
• We can queue messages to an object

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Associations

• An association is some form of a link that two or
  more objects share
• An association can be unidirectional going
  one way, like a tv remote to the tv, or
  bidirectional such as a console and a joypad
  when the joypad rumbles

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Aggregation

• An aggregation is an a collection of objects that
  work together
• e.g. a car is an aggregate of an engine,
  chassis, wheel, etc.
• A more hardcore version of aggregation is
  composition. The term is used when an
  aggregation is useless without all of its
  components.

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Intermission
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Practical OO
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Theory in practice

• What youll learn in this lecture -
• Class Visualisation
• Attributes
• Operations
• Responsibilities and Constraints
• Determining Classes

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Class Visualisation

• A class is a box containing the name of the
  class.
• If the class has two words describing it, join
  them and take the first letters of each word and
  uppercase them.

Saloon Car
SaloonCar
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CV Packages

• A UML construct (technique) known as the package,
  plays a role in the name.
• A package is a way of organising classes
  together.
• The package is represented by a tab on top of the
  folder.

Vehicles
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CV Pathnames

• If the SaloonCar is part of a package called
  Vehicles, you can give it the full name of
  VehiclesSaloonCar.
• The double colons separate the name of the
  package from the name of the class.

Vehicles SaloonCar
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Attributes

• An Attribute is a property of the class.
• It describes the type of data an instance of the
  class holds.
• A single word attribute is written in lower case.
  E.g. colour. Two word attributes are written in
  camel case, except the first word. E.g.
  brandName.

SaloonCar
colour brandName engineSize
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Attributes - Instantiation

• A named instance i.e. an object, can be written
  out like the example opposite. Note the underline
  in the title, and the single colon.
• An attribute can also have defaults. They are
  written similarly to the named instance, but with
  a normal title.

MyCarSportsCar
colour Silver brandName Lotus engineSize
1796
SportsCar
colour brandName Lotus engineSize
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Operations

• An operation is something a class can do, or
  something that can be done to the class.
• Operation names are written in the same way as an
  attribute, but with appended parenthesis.

SportsCar
colourbrandName engineSize
startEngine() removeHood() windWindow() turnOnRadi
o()
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Operations - Signature

• You can indicate additional information in
  operations.
• Included in the parenthesis are parameters, data
  that the operation needs .
• If a colon follows an operation, with a data type
  following that, then that is the return value.

SportsCar
colourbrandName engineSize
startEngine( E Boolean) removeHood( H
String) windWindow( W Int) turnOnRadio( R
int) Boolean
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Class Task 2

• Again working on your own
• Look again at the list of classes you identified,
  do you want to make any changes?
• For each of the classes you identified, draw a
  visual representation showing class name,
  attributes and operations.

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Visualising make it easy!

• When dealing with many classes on a single page,
  its ok to remove the attributes and operations
  for clarity.
• To highlight some components of the class, leave
  them in, and signify others with three periods.

SportsCar
SportsCar
colour
startEngine( E Boolean)
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Visualising - Stereotypes

• You can use stereotypes to help understand the
  class.
• The stereotype is enclosed within guillemets
  the angled brackets.
• Stereotypes are very flexible constructs, you
  can use them for anything that helps the user to
  understand.

SportsCar
ltlt id gtgt serialNo ltlt model data
gtgt colourbrandName engineSize
startEngine( E Boolean) removeHood( H
String) windWindow( W Int) turnOnRadio( R
int) Boolean
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Responsibilities

• A classes Responsibility can be denoted with
  another box underneath the class.
• It shows what the class must do.
• A Constraint is a limitation of the attribute
  or operation.
• It is shown by a sentence in curly braces.

SportsCar
serialNo
startEngine( E Boolean)
can only do it with ignition on
ResponsibilityTo deliver its passengers to
another destination
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Notes

• A note can be added to any part of the class, or
  the class itself.
• The note icon has a dotted line which connects
  the note to what the note is about.

A note
SportsCar
serialNo
startEngine
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Finding Classes

• Classes are the vocabulary of any area of
  knowledge.
• They are the nouns in any sentence.
• Attributes are the nouns describing nouns, and
  operations, the verbs.
• After you have highlighted each class, you can
  ask the client what attributes they contain and
  operations they perform.

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Intermission
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Relationships in the UML
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Relationships

• What youll learn in this section -
• Associations
• Multiplicity
• Qualified Associations
• Reflexive Associations
• Inheritance and Generalisation
• Dependencies

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Associations

• Relationships exist between classes.
• Mostly, a class has a relationship with multiple
  classes
• Each relationship can be identified by an arrowed
  line with an explanation between classes
• The class can signify a role by a name underneath
  the relationship
• Relationships can go both ways

Jumps from
Skydiver
Plane
Jumps from
Skydiver
Plane
passenger
vehicle
Jumps from
Skydiver
Plane
Gives a lift to
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Constraining associations

• A constraint can be placed on the relationship
• The Or relationship can be used to associate
  classes by rules

Jumps from
Plane
Skydiver
Jumps from
Helicopter
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Association Classes

• An association class is a class that represents a
  relationship and can have attributes and
  operations
• An instantiated class (an object) can represent
  their relationships through links

Skydiver
Plane
Jumps from
Manifest
Ticket
Jumps from
Rob skydiver
Nomad Plane
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Multiplicity

• Multiplicity is very similar to ERDs
• Each class can have a number of other classes
  associated with it
• It represents how you can access the data held in
  classes
• You may use Qualifiers to determine a
  particular key which you can use to identify the
  class that owns another class

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1

Skydiver
Plane
Jumps from
1
1
Skydiver
Chute
uses
1
1,2
Skydiver
Tickets
Can buy
1,2

Can have
Skydiver
Tickets
Skydiver_id
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Reflexive Associations

• Sometimes a class can have a relationship with
  itself
• For example, a pilot can be the pilot or an
  occupant
• This is represented by a line drawn to itself

Occupant
pilots
1
skydiver
0..23
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Inheritance Generalisation

• They both mean categorisations of classes into
  general classes
• A generalised or parent class holds attributes
  and operations that all of their child classes
  inherit
• Discovering inheritance is an experience thing
  use your knowledge of the real world to make it
  happen
• Abstract classes can never become objects, but
  you can inherit from them for convenience

Person
Male
Female
Neutral
Skydiver
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Dependencies

• A dependency is a form of relationship when a
  class need to use another object to perform its
  function
• It is represented by a dashed line into the other
  class

Engine
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Aggregations

• An aggregation is relationship between classes,
  that indicates that a class is made up from
  multiple classes
• For example, a car is made up from an engine,
  seats, chassis, etc
• A class that is part of an aggregation has a
  diamond along its connecting line

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Car
1
1
1..5
Seat
Engine

1
Ignition System
Fuel System
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Aggregation Constraints

• A constraint of an aggregation is indicated by a
  dashed line going between the two optional
  components
• In this case, a car can have a hardtop or a soft
  top but not both

Car
1
1
1
or
Soft top
Hard top
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Composites

• A composite is a strong aggregation
• A black diamond represents that the relationship
  must contain the composite classes

Kettle
1
1
1
Heating Element
Container
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Contexts

• A context puts classes together in a rational
  way. For example, a skydiver has a parachute,
  which contains a canopy and lines
• There are two versions of context diagrams one
  being a composite context diagram (a class that
  owns all the other classes) and a system context
  diagram (which shows where the context fits in
  with the rest of the system)

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Kettle
Is located in the bottom of gt
1

Heating Element
Container
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Interfaces Realisations

• Sometimes, youll create a class that requires
  some functionality of another class, but isnt
  directly related to them
• In this case, remove the functionality from both
  and create an interface
• An interface is a common set of functionality
  that can be applied to any class
• The relationship is called a realisation

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Email
ltlt Interface gtgtMessage
Email
Name Subject
Send() Delete()
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Visibility

• Visibility is how accessible components
  (attributes operations) of the class are
• A components visibility can be public (),
  private (-) or protected ()
• A public component can be accessed by any other
  component in the system, whereas a private
  component is not accessible by anyone
• A protected component can be accessed by any
  component that sub classes the original

Email
Email Recipient -Sender
Send() Delete() updateProfile()
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Scope

• Scope is relevant to attributes and operations
  and how they are accessed in the system
• In instance scope, the component is available
  to the class only
• In classifier scope, the component is
  available across all instances of the class.
  Classifier scope components are underlined

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Class Task 3

• Working in groups, attempt to construct a full
  class-diagram for the proposed system.