IMS5024 Week 3 Semester 2, IMS 5024 Object orientation (1)

IMS5024 Week 3 Semester 2, Content What is object orientation? Example of object oriented analysis Place in ISD Evaluation of Object orientation Reading list

IMS5024 Week 3 Semester 2, History of object orientation Developed in the 1970’s Various places – computer architecture, operating systems, databases, cognitive science, artificial intelligence Programming language Simula and Smalltalk

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, Object orientation describe: Structure (data) Behaviour Function (too a lesser degree?) Of Objects

IMS5024 Week 3 Semester 2, Object orientation help to present: The object State Behaviour described by actions Of objects

IMS5024 Week 3 Semester 2, Other characteristics Abstraction Inheritance Encapsulation Polymorphism

IMS5024 Week 3 Semester 2, Techniques used in Object orientation Object model – object diagrams Dynamic model – state transition diagrams Functional model – action data flow diagrams, use case

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, Class ‘A group of object exhibiting the same characteristics such as structure and behaviour’ Abstraction Inheritance

IMS5024 Week 3 Semester 2, Message/signal Objects interact with one another through signal or message Signals are generated by an event Event occur when the object’s state changes Change the state of an object through an objects methods Has to conform to the interface of the object

IMS5024 Week 3 Semester 2, Notation for a class/object Object name Attributes Processes/Methods Public part

IMS5024 Week 3 Semester 2, Aggregation/ whole/part class Car WheelEngineBody Cylinder Cam shaft

IMS5024 Week 3 Semester 2, Generalisation/Specialisation Account Basic account Checking account Loan Service Account

IMS5024 Week 3 Semester 2, Steps Develop a summary paragraph Identify objects of interest Identify method/processes Define attributes of objects Perform class analysis Draw state transition diagram

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, Example of declarative sentences

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, Example of objects

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, Example of processes

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, Example of attributes

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, Example of class analysis

IMS5024 Week 3 Semester 2, Thinking in Object orientation Hard Vs Soft ?? Perspective –Objective vs Subjective –Nature of the organisation

IMS5024 Week 3 Semester 2, Evaluation of Object oriented modelling Problem orientedProduct 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

IMS5024 Week 3 Semester 2, 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

IMS5024 Week 3 Semester 2, 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??

IMS5024 Week 3 Semester 2, Object orientation view of ISD Development group Objectives Environment Object system Object system Change process Hirschheim et al see reading list

IMS5024 Week 3 Semester 2, 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 Jacobsen, I., Booch, G., Rumbaugh, J. (1999). The unified software development process. Addison Wesley Longman, Inc. USA. Chapter 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