Modelling Business Systems 9

1. Modelling Business Systems 9 Other Systems Methods CB1004 Modelling Business Systems 9

2. Structure Oriented Development • Tasks are: • Identify the data structures that make up the information • Analyse the relationship between the components in terms of sequence, iteration and condition • Define the processes to produce the components of the data structure • Map the structural relationship of the data into a control hierarchy for the processes CB1004 Modelling Business Systems 9

3. Jackson Systems Design (JSD) • Seen as a bottom-up approach • Ignores conventional views of the systems life cycle (SLC) • Some authors e.g. Avison & Fitzgerald (1988) think it is not a complete method e.g. does not cover database design CB1004 Modelling Business Systems 9

4. JSD Stage 1 • (Entity/action) modelling • Identifies the entities and actions in the real world relevant to the IS • Entities • Identifying these is difficult but they are often the nouns used in the description e.g. customer, supplier, order etc • Must be unique • Must perform actions or have actions performed upon them CB1004 Modelling Business Systems 9

5. Actions • Must take place at a point in time i.e. not be continuous i.e. conclude a sale NOT selling • Must take place in the real world - not be part of the information system that seeks to control it e.g. engage supplier NOT print supplier list CB1004 Modelling Business Systems 9

6. JSD Structure Diagram Supplier Deregister Product movement * Register Receipt o Return o CB1004 Modelling Business Systems 9

7. JSD Stage 2 • Network Stage • Initial model stage • Specify an information system to model and control these real world entities and actions (processes) • Produces a systems specification diagram (SSD) • Processes identified in previous stage Purchasing and supply Material and Parts control CB1004 Modelling Business Systems 9

8. SSD • Now consider the connections • Data stream connection – stream of sequential message e.g. text being keyed in connects two processes Parts request Parts for issue Purchasing and supply Material and Parts control CB1004 Modelling Business Systems 9

9. SSD • State vector connection – one process inspects the state of another process at a particular point in time • Produces a simulation model of the real world SV Purchasing and supply Stock CB1004 Modelling Business Systems 9

10. JSD 2 cont • Next step – function step • Define in structure language the processes Open file While not end of month Do Write page heading Initialise line count While not end of page Do Write line Increment line count End while ……… CB1004 Modelling Business Systems 9

11. Specify the required outputs and the defined inputs • Result is a logical model • Does not consider • when information is needed • when processes should run CB1004 Modelling Business Systems 9

12. JSD Stage 3 • Implementation stage • Converts the SSD into software • Structure code basically similar to high level programming languages, hence conversion virtually automatic • Stage essentially about allocation and arrangement of processes and processors CB1004 Modelling Business Systems 9

13. Object Oriented Development • Creates a systemic software model of a real world situation made up of objects • Similarity between objects and entities (JSD) • But an object can be a concrete or abstract identifiable element or component of the problem domain (Booch 1991) CB1004 Modelling Business Systems 9

14. Object – other important kinds of objects are inventions of the design process whose collaborations with other objects serve as mechanisms that provide some higher levelbehaviour (Halbert & O’Brian 1988) • Inventions = concepts • The design process – not abstract or impersonal, people make them work • Higher level behaviour = holistic concept placed in the context of a hierarchy CB1004 Modelling Business Systems 9

15. OOS – major features • Hierarchy • Already seen the term ‘part of’; in OOS get ‘kind of’ – enables us to classify objects according to shared characteristics at increasing levels of abstraction • Enables reuse of software of commonly shared characteristics • Reusable code • Allows for evolutionary systems development based on learning CB1004 Modelling Business Systems 9

16. Objects and their properties • State • Look at a specific object – quantity sold • Property is static because it is unlikely to be changed to anything else e.g. quantity bought • Value is dynamic – different values through time • Behaviour • Changes of state it undergoes as a result of passing and receiving messages to and from other objects CB1004 Modelling Business Systems 9

17. Objects and their properties • Object identity • More than the name • Includes the properties that make it what it is • Relationships • Using relationships – concerned with process • Objects seen in terms of how they affect one another • Control function might send a message to another object to check on a value and receive feedback information • Containing relationships- concerned with structure • Aggregation of relationships within a systemic hierarchy • A cupboard consists of components e.g doors CB1004 Modelling Business Systems 9

18. Relationships Cupboard Stock controller Door Container unit SC uses the cupboard to check its availability Cupboard has a containing relationship with its components CB1004 Modelling Business Systems 9

19. Objects and their properties • Class and class hierarchies • Depends on the view of the developer • Which is the odd one out: Dog, cat television? • View • Animal or • Which needs a licence • Class depends on the properties CB1004 Modelling Business Systems 9

20. Class and inheritance • A class shares the structure or behaviour defined in one (single) or more (multiple) other classes (super classes) CB1004 Modelling Business Systems 9

21. Inheritance Animals Reptiles Mammals Lizards Snakes Cats Dogs 4 legged animals CB1004 Modelling Business Systems 9

22. Single inheritance • Cats and dogs inherit behaviour e.g. suckling young from the mammal super class • Multiple inheritance • Structure and behaviour of being a 4-legged animal that suckles its young CB1004 Modelling Business Systems 9

23. Meta-class relationships • Classes can themselves be regarded as objects • Leads to classes of classes • Classes are objects BUT objects are not classes CB1004 Modelling Business Systems 9

24. The OO model • Identify classes and objects • Depends on the purpose of the development so no particular technique • Indicated by nouns or names • Defining the semantics of classes and objects • Establish activities and behaviour; again no technique • Indicated by verbs CB1004 Modelling Business Systems 9

25. Identifying relationships between classes and objects • Classes – identify inheritance, using and other relationships • Objects – establish static and dynamic properties • Implement classes and objects • Create the software model • OO is NOT a structured method CB1004 Modelling Business Systems 9

26. Some OO diagramming techniques # • Class diagrams • What classes exist and their relationships • Object diagrams • Specifies mechanism used to regulate how objects collaborate • State Transition Diagrams • Specifies how the time ordering of external events can affect the state of each instance of a class • Module diagrams • Physical packaging of classes and objects into software modules CB1004 Modelling Business Systems 9

27. OO Software • OO forms of Pascal • C++ (development of C) • CLOS (Common Lisp Object System) • Smalltalk • Eiffel CB1004 Modelling Business Systems 9

28. Prototyping • First version of a system to be modified after testing • Guide to development of other components within the system • Concerned • Not with does it work? • BUT • does it work the way you want it to? CB1004 Modelling Business Systems 9

29. Prototyping • Useful in the context of structured design to develop e.g. printouts, screens etc • Uses 4GLs • GUIs (graphical user interfaces) CB1004 Modelling Business Systems 9

30. Integrated methods • Developed as a result of problems with individual approaches • Multiview (Wood-Harper 1985) # • Analysis of human activates • SSM as far as the conceptual model • Analysis of entities, functions and events • Follows mainstream IS development concepts as previously mentioned CB1004 Modelling Business Systems 9

31. Multiview cont. • Analysis and design of sociotechnical system • Recognises that all change involves conflict of interest • Looks at employees needs and wants • Creates a fit between the employee and employer • Knowledge fit – employees should believe their skills and worth are being adequately used • Psychological fit – conforming to employees view of their aspirations • Efficiency fit – balancing financial rewards to employees against requirements of the employer • Task structure – reflecting the success in making the job appropriately demanding and fulfilling for the employee • Ethical fit between employee and employer CB1004 Modelling Business Systems 9

32. Multiview cont. • Design of human computer interface • How computers and humans will interact • Design of technical subsystems • Choice of hardware and software CB1004 Modelling Business Systems 9