1. IMS5024 Week 3 Semester 2, 2004 1 IMS 5024 Object orientation (1)

2. IMS5024 Week 3 Semester 2, 2004 2 Content What is object orientation? Example of object oriented analysis Place in ISD Evaluation of Object orientation Reading list

3. IMS5024 Week 3 Semester 2, 2004 3 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

4. IMS5024 Week 3 Semester 2, 2004 4 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

5. IMS5024 Week 3 Semester 2, 2004 5 Object orientation describe: Structure (data) Behaviour Function (too a lesser degree?) Of Objects

6. IMS5024 Week 3 Semester 2, 2004 6 Object orientation help to present: The object State Behaviour described by actions Of objects

7. IMS5024 Week 3 Semester 2, 2004 7 Other characteristics Abstraction Inheritance Encapsulation Polymorphism

8. IMS5024 Week 3 Semester 2, 2004 8 Techniques used in Object orientation Object model – object diagrams Dynamic model – state transition diagrams Functional model – action data flow diagrams, use case

9. IMS5024 Week 3 Semester 2, 2004 9 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

10. IMS5024 Week 3 Semester 2, 2004 10 Class ‘A group of object exhibiting the same characteristics such as structure and behaviour’ Abstraction Inheritance

11. IMS5024 Week 3 Semester 2, 2004 11 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

12. IMS5024 Week 3 Semester 2, 2004 12 Notation for a class/object Object name Attributes Processes/Methods Public part

13. IMS5024 Week 3 Semester 2, 2004 13 Aggregation/ whole/part class Car WheelEngineBody Cylinder Cam shaft

14. IMS5024 Week 3 Semester 2, 2004 14 Generalisation/Specialisation Account Basic account Checking account Loan Service Account

15. IMS5024 Week 3 Semester 2, 2004 15 Steps Develop a summary paragraph Identify objects of interest Identify method/processes Define attributes of objects Perform class analysis Draw state transition diagram

16. IMS5024 Week 3 Semester 2, 2004 16 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

17. IMS5024 Week 3 Semester 2, 2004 17 Example of declarative sentences

18. IMS5024 Week 3 Semester 2, 2004 18 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

19. IMS5024 Week 3 Semester 2, 2004 19 Example of objects

20. IMS5024 Week 3 Semester 2, 2004 20 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

21. IMS5024 Week 3 Semester 2, 2004 21 Example of processes

22. IMS5024 Week 3 Semester 2, 2004 22 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

23. IMS5024 Week 3 Semester 2, 2004 23 Example of attributes

24. IMS5024 Week 3 Semester 2, 2004 24 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

25. IMS5024 Week 3 Semester 2, 2004 25 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

26. IMS5024 Week 3 Semester 2, 2004 26 Example of class analysis

27. IMS5024 Week 3 Semester 2, 2004 27 Thinking in Object orientation Hard Vs Soft ?? Perspective –Objective vs Subjective –Nature of the organisation

28. IMS5024 Week 3 Semester 2, 2004 28 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

29. IMS5024 Week 3 Semester 2, 2004 29 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

30. IMS5024 Week 3 Semester 2, 2004 30 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??

31. IMS5024 Week 3 Semester 2, 2004 31 Object orientation view of ISD Development group Objectives Environment Object system Object system Change process Hirschheim et al see reading list

32. IMS5024 Week 3 Semester 2, 2004 32 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