Object-Oriented Development

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Object-Oriented Development
By Grady Booch
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Abstract

• Object-oriented development is a
  partial-lifecycle software development method
  which the decomposition of a system is based on
  the concept of an object
• This method is fundamentally different than
  Traditional functional approaches to design

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Abstract continues

• Serves to help manage the complexity of massive
  software-intensive systems

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Introduction

• Object-oriented programming is what structured
  programming was in 1970s
• Object-oriented approach to software design in
  which the decomposition of a system is based upon
  the concept on an object

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Continued

• An object is an entity whose behavior is
  characterized by the action that it suffers and
  that requires of other objects
• Object oriented development is different than
  traditional functional methods

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Functional method

• Fortran, Cobol, Pascal
• Each module represents a major step in the
  overall process
• Tend to consist of collections of programs,
  because they are the only building blocks
  available

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Continued

• Subroutines are not well suited to the
  description of abstract objects. This is a
  serious drawback

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Object-oriented method

• Ada and Smalltalk
• subprogram as an elementary building block
• In Ada, Package and task are major elements
• Package is used to create new objects and classes
  of objects

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Continued

• Task express concurrent objects and activities in
  a natural way
• Package and subprograms help to better build
  abstraction of the problem space by permitting a
  more balanced treatment between nouns and verbs

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Nouns and Verbs

• Nouns are objects
• Verbs are operations

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functional method Limitations

• Do not effectively address data abstraction and
  information hiding
• Generally inadequate for problem domains with
  natural concurrency
• Often not responsive to changes in the problem
  space
• OO approach mitigate these problems

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A cruise control design

• Inputs to the system
• System on/off
• If on, cruise control maintains the speed
• Engine on/off
• Cruise control only active if engine is on
• Pulse from wheel
• One pulse for every revolution
• Accelerator
• How far it has been pressed

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Continued

• Brake
• when pressed, cruise control is turned off
• Increase/Decrease Speed
• If only the cruise control system is on
• Resume
• Resume the last maintained speed
• Clock
• Timing pulse every millisecond

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Continued

• Output from the system
• Throttle
• Digital value for the engine throttle setting

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Cruise Control Hardware Block Diagram
System on/off
Engine on/off
Pulse from Wheel
Cruise- Control System
Accelerator
Throttle
Brake
Increase/decrease speed
Resume speed
Clock
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Pulse
Wheel
Calculate Current Speed
Current speed
Current speed
Clock tick
Clock
On/Off
Calculate Desired Speed
Driver
Desired speed
Desired speed
Incr/Decr
Resume
Set Brake State
Brake State
Brake
Brake State
On/Off
Brake State
On/Off
Engine
Calculate Throttle Setting
Desired speed
Value
Current Speed
Throttle Setting
Accel
Throttle
Throttle Setting
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Cruise Control System
Get Desired Speed
Get Current Speed
Get Brake State
Calculate Throttle Setting
Put Throttle Value
Functional Decomposition
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Wheel
Clock
Driver
Current Speed
Brake
Desired Speed
Engine
Throttle
Object Oriented Decomposition
Accelerator
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Object-Oriented Development

• Major steps in Object-oriented development
• Identify the objects and their attributes
• Identify the operations suffered by and required
  of each object
• Establish the visibility of each object in
  relation to other objects
• Establish the interface of each object
• Implement each object

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Identify the objects and their attributes

• Recognition of major actors, agents, and servers
  in the problem space plus their role in our model
  of reality
• The objects identify is this step derive from the
  nouns used in describing the problem space
• Establish classes of objects for similar objects

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Identify the operations suffered by and required
of each object

• Serves to characterize the behavior of each
  object or class of objects
• Establish the static semantics of the object by
  determining the operations that may be
  meaningfully performed on the object of objects
• Establish the dynamic behavior of object by
  identifying the constraints upon time or space
  that must be observed

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Establish the visibility of each object in
relation to other objects

• We identify the static dependencies among objects
  and classes of objects
• In other words, what objects see and are seen by
  a given objects
• The purpose of this step is to capture the
  topology of objects from our model of reality

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Establish the interface of each object

• Produce a module specification, using some
  suitable notation (Ada, Smalltalk, etc, )
• This captures the static semantics of each object
  or class of objects that we established in
  previous step
• This specification serves as a contract between
  the clients of an object and the object itself
• In other words, the interface forms the boundary
  between the outside view and the inside view of
  an object

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Implement each object

• Involves choosing a suitable representation for
  each object or class of objects
• Implementing the interface from previous step
• Involves decomposition or composition if an
  object is found to consist of several objects
• In this case we repeat our method to further
  decompose the object

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Useful points

• Object-oriented development is a
  partial-lifecycle method
• It focuses upon the design and implementation
  stages of software development
• It is necessary to couple object-oriented
  development with appropriate requirements and
  analysis methods in order to help create or model
  of reality

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Major Goals in developing object Based software

• To reduce the total life-cycle software cost by
  increasing programmer productivity and reducing
  maintenance cost
• Implement software system that resist both
  accidental and malicious corruption attempts

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Properties of an Object

• Object is an entity that
• Has state
• Is characterized by the actions that it suffers
  and that it requires of other objects
• Is an instance of some class
• Is denoted by a name
• Has restricted visibility of and by other objects
• May be viewed either by its specification or by
  its implementation

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Object Classification

• Actor
• Suffers no operation but only operates upon other
  objects
• Agent
• Serves to perform some operation on behalf of
  another object and in turn may operate upon
  another object
• Server
• Suffers operation and may not operate upon other
  objects

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Class

• An object is a unique instance of some class
• A class denotes a set of similar but unique
  objects
• Class serves to factor the common properties of a
  set of objects and specify the behavior of all
  instances

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Inheritance

• Permits a hierarchy of classes
• All objects are an instance of a class, which is
  a subclass of another class (and so on)
• Subclass has the same operations defined by the
  superclass
• May also add operation, modify existing
  operation, and hide operation from the superclass

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Two views to each Objects

• Outside View
• Serves to capture the abstract behavior of the
  object
• An object can interact with other objects by just
  knowing its outside view
• Implementation does not need to be present for
  interaction with the object
• Inside View
• Indicates how the behavior is implemented and it
  is hidden form other objects

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Ada and Object-Oriented Development

• Classes of objects are denoted by packages that
  export private or limited private types
• Objects are denoted by instances of private or
  limited private types or as packages that serve
  as abstract state machined
• Objects state resides either with a declared
  object or in the body of a package

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Continued

• Operations are implemented as subprograms
  exported from a package specification generic
  formal subprogram parameters serve to specify the
  operations required by an object
• Visibility is statistically defined through unit
  context clauses
• Separate compilation of package specification and
  body support the tow views of an object
• Tasks and task types may be used to denote actor
  objects and classes of objects

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Name_X
Name_Y
Name_B
Object
Object
Name_A
Package
Type
Object
Operation
Operation
Names, Objects and Classes Interaction of the
points in the previous slide
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Symbols of OOD
Generic Subprogram
Task
Subsystem
Generic Package
Subprogram
Package
Object
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• These symbols can be connected by a direct line
• A line connects object A to B, this denotes
  object A depends on object B

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Design Case Study

• A collection of free-floating Buoys
• Buoys collect air and water temperature
• Collect wind speed
• Collect location data through variety of sensors
• Each equipped with a radio transmitter to
  broadcast weather and location in formation as
  well as an SOS message
• Each equipped with a radio receiver to receive
  requests from passing vessels

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• Some equipped with a red light, which may be
  activated by vessel during a sea-search
  operations
• If a sailor is able to reach the buoy, he or she
  may flip a switch on the side to initiate an SOS
  broadcast

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• Buoys

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Software Requirements

• Maintain current current wind temperature, and
  location in formation wind speed readings are
  taken every 30 seconds temperature readings
  every 10 seconds and location every 10 seconds
  wind and temperature wind and temperature values
  kept as a running average
• Broadcast current wind, temperature and location
  information every 60 seconds

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• Broadcast wind, temperature, and location
  information from the past 24 hours in response to
  requests from passing vessels
• Activate or deactivate the red light based on a
  request from a passing vessel
• Continuously broadcast an SOS signal after a
  sailor engages the emergency switch this takes
  priority over all other broadcast and continues
  until reset by a passing vessel

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Pulse
Clock
Location Sensor
Water Temp Sensor
Air Temp Sensor
Wind Speed Sensor
Value
Value
Value
Value
Calculate Location
Calculate Average
Calculate Average
Calculate Average
Pulse
Avg. value
Avg. value
value
Avg. value
Sensor Data Bases
Radio Receiver
Broadcast Message
Request
Wind/Location Data
Radio Transmitter
SOS Message
State
Set Light State
SOS Request
Emergency Switch
State
Red Light
Host at see Buoy data flow diagram
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Objects

• Clock
• Provides the stimulus for periodic actions
• Wind Speed sensor
• Maintains a running average of wind speed
• Air Temperature Sensor
• Maintains a running average of air temperature
• Water Temperature Sensor
• Maintains a running avg. of water temperature
• Location Sensor
• Maintains the current buoy location
• Sensor Database
• Serves to store weather and location history

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• Radio Receiver
• Provides a channel for requests from passing
  vessels
• Radio Transmitter
• Provides a channel for broad cast of weather and
  location reports as well as SOS messages
• Emergency Switch
• Provides the stimulus for the SOS signal
• Red Light
• Controls the activity of the emergency light
• Message Switch
• Serves to generate and arbitrate various
  broadcast messages

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Clock
Air Temp Sensor
Wind Speed Sensor
Water Temp Sensor
Location Sensor
Sensor Data Base
Radio Receiver
Radio Transmitter
Message Switch
Red Light
Host at see buoy objects
Emergency Switch
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Operations Suffered by an Object

• Clock
• None
• Wind Speed Sensors
• Take Sample
• Air Temperature Sensors
• Take Sample
• Water Temperature Sensors
• Take Sample
• Location Sensor
• Take Sample

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• Sensor Database
• Put value
• Get value
• Radio Receiver
• None
• Radio Transmitter
• Broadcast SOS
• Broadcast Weather/Location report

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• Emergency Switch
• None
• Red Light
• Set State
• Message Switch
• Request History Report
• Request SOS

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Operations Required from an Object

• Clock
• Force Sample
• Force Periodic Report
• Wind Speed Sensors
• Put Value
• Air Temperature Sensors
• Put Value
• Water Temperature Sensors
• Put Value
• Location Sensor
• Put Value

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• Sensor Database
• None
• Radio Receiver
• Force History Report
• Set Light State
• Radio Transmitter
• None

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• Emergency Switch
• Force SOS
• Red Light
• None
• Message Switch
• Send Weather/Location Report
• Send SOS
• NOTE There is a balance between the operations
  suffered by and required of all objects. For
  each operation suffered by an object, we have
  other object or set of objects that require that
  action

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Ada Representation

• generic
• type value is digits lt gt
• with procedure Put_Value (The_Value in Value)
• package Air_Temperature_Sensors is
• type Sensor is limited private
• procedure Take_Sample (The_Sensor in out
  Sensor)
• private
• type Sensor is
• end Air_Temperature_Sensors

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Clock
Location Sensor
Water Temp Sensors
Wind peed Sensors
Air Temp Sensors
Sensor Data Base
Message Switch
Radio Transmitter
Radio Receiver
Reports
Emergency Switch
Red light
Host at see buoy objects
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Conclusion

• The greatest strength of an object-oriented
  approach to development is that it offers a
  mechanism that captures a model of the real
  world.
• This leads to improved maintainability and
  understandability of systems whose complexity
  exceeds the intellectual capacity of a single
  developer or a team of developers