IMS 5024

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IMS 5024

• Object orientation (1)

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Content

• Individual assignment date
• Group assignment
• What is object orientation?
• n
• n
• Place in ISD
• Evaluation of Object orientation
• Reading list

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Reminder - Date for the individual assignment

• 30 August 2001 in class

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History of object orientation

• Developed in the 1970s
• Various places computer architecture, operating
  systems, databases, cognitive science, artificial
  intelligence
• Programming language Simula and Smalltalk

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Why popular now

• Popularity of graphical interfaces
• Acceptance of C
• Cost cutting by business
• Increase in the power of technology
• Shift from mainframes to distributed computing

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Object orientation describe

• Structure (data)
• Behaviour
• Function (too a lesser degree?)
• Of Objects

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Object orientation help to present

• The object
• State
• Behaviour described by actions
• Of objects

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Other characteristics

• Abstraction
• Inheritance
• Encapsulation
• Polymorphism

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Techniques used in Object orientation

• Object model object diagrams
• Dynamic model state transition diagrams
• Functional model action data flow diagrams, use
  case

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Object

• is something to which action is directed, it has
  an identity, a state and exhibits behaviour
• Can be anything concrete or conceptual
• Is an abstraction of the real world

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Class

• A group of object exhibiting the same
  characteristics such as structure and behaviour
• Abstraction
• Inheritance

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Message/signal

• Objects interact with one another through signal
  or message
• Signals are generated by an event
• Event occur when the objects state changes
• Change the state of an object through an objects
  methods
• Has to conform to the interface of the object

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Notation for a class
Object name
Public part
Attributes
Processes/Methods
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Aggregation/ whole/part class
Car
Wheel
Engine
Body
Cylinder
Cam shaft
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Generalisation/Specialisation
Account
Basic account
Checking account
Loan
Service Account
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Steps

• Develop a summary paragraph
• Identify objects of interest
• Identify method/processes
• Define attributes of objects
• Perform class analysis
• Draw state transition diagram

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Develop a summary paragraph

• Write declarative sentences
• Write each sentence on its own line
• Review paragraph carefully to ensure
• All desired functions are represented
• All major information and processes are
  identified
• All sentences are at the same level of
  abstraction and importance

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Example of declarative sentences
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Identify objects of interest

• Underline all nouns in summary paragraph
• List underlined nouns separately
• Evaluate each noun to ensure it is an object
• Determine whether object is solution or problem
  space
• Name each object in solution space

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Example of objects
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Identify processes

• Circle all verbs in the summary paragraph
• List verbs on a separate paper
• Evaluate each verb
• Determine whether the process is solution or
  problem space
• Name each unique process in the solution space
• Assign object to verbs if the objects is
  transformed or read by the process
• Evaluate object assignments

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Example of processes
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Define attributes of objects

• Attributes named fields or properties that
  describe a class or object
• A set of attributes values describe an object or
  instance
• Primary key unique set of values

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Example of attributes
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Define attributes of processes

• Assign attributes which were set aside during
  object or process definition
• Review the original problem description and any
  notes
• Review the summary paragraph to find implied
  attributes

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Perform class analysis

• Look for shared attributes and processes across
  class/objects to define inheritance class
• Evaluate the class/objects for specialization
• Evaluate the class/objects for component part
  relationships
• Define common class objects
• Define meta-class

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Example of class analysis
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Thinking in Object orientation

• Hard Vs Soft ??
• Perspective
• Objective vs Subjective
• Nature of the organisation

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Evaluation of object orientated modelling
Problem oriented Product oriented
Concep-tual Structured analysis Entity relationship modelling Logical construction of systems Modern structured analysis Object oriented analysis Structured design Object oriented design
Formal PSL/PSA JSD VDM Levels of abstraction Stepwise refinement Proof of correctness Data abstraction JSP Object oriented programming
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Advantages/ Benefits of object orientation

• It unifies many aspects of the information
  systems development process.
• It facilitates re-use of software code make
  application development quicker and more robust
• Ability to tackle more complex problems
• Improve user/analyst relations ???
• Improvement in the consistency of results
• Represent factors for change in the model

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Disadvantages of object orientation

• Only now starting to be used
• Case tools are not readily available
• Not easily understood by novice users
• Difficult to master for some analysts designers
  programmers
• Inefficiency (need a lot of power)
• Others??

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Object orientation view of ISD
Objectives
Development group
Object system
Object system
Change process
Environment
Hirschheim et al see reading list
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Reading for next week

• Iivari, J. (1995) Object orientation as
  structural, functional and behavioural modelling
  a comparison of six methods for object-orientated
  analysis. Information and Software Technology,
  vol 37, no. 3, pp. 155-163
• Jacobsen, I., Booch, G., Rumbaugh, J. (1999). The
  unified software development process. Addison
  Wesley Longman, Inc. USA. Chapter 3, 7.4.3.
• Rumbaugh, J., Blaha, M., Premerlani, W., Eddy,
  F., Lorensen, W. (1991) Object oriented modeling
  and design. Prentice Hall, Inc. USA. Chapter 5.1
  5.3