System Development CyclePlanning, Design and Implementation represent themain steps in what is in a number of courses - adevelopment cycleIn IPT it is the ‘system development cycle’ (which wouldhave been a better topic heading)In SDD it is the ‘software development cycle’It is basic problem-solving methodology: Understand the problem Plan/research/analyse/make decisions Design a solution Implement the solution Test/evaluate/refine/maintain the solution
The IPT System Development Cycle (Grover) Understand the problem Outcome: Project plan Make decisions Outcome: Design option selected Revision of system - Design a solution cycle begins again Outcome: New system created Implement the solution Outcome: New system is used Test, evaluate and maintain the solution
System Development CycleKeeping a system up-to-date and satisfactory is a continuouscycleDifferent texts have different interpretations of the way eachstage of ‘Planning, Design and Implementation’ is broken downinto sub-topicsI have used the syllabus here as the arbiter in the debate e.g.analysis of the existing system is in the ‘understanding theproblem to be solved’ part of Planning, not in the ‘makingdecisions’ part according to the syllabus but not according tosome other authorsIf in doubt follow the syllabus and you can’t be accused ofgetting it wrong! e.g. ‘Planning’ = ‘Understand the Problem’ +‘Make Decisions’Each course also has a set of tools used fordocumenting/modeling
Modeling ToolsModeling/documentation tools specified in both the IPT andSDD syllabi are: Data flow diagrams Systems flowcharts Storyboards Data dictionaries Gantt chartsThose in IPT only are Decision tables Decision trees Block diagrams / Organisational charts / Hierarchical chartsThose in SDD only are IPO Structure charts Algorithm flowcharts
Modeling ToolsStudents need to know what each toolis used for (and not used for) and atwhich stage of the cycle it is appropriateThey are more likely to have to interpretthe resulting diagrams, charts, etc thancreate them for complicated casestudies but can expect to do either forsimpler ones
Understand the ProblemUnderstanding the problem involves Collecting data re problems with the existing system to discover needs of users and participants. Students must understand features, advantages and disadvantages of: Interview Surveys/Questionnaires Observation Analysing the existing system (how, what, who) and using modeling tools to represent it. Students must be able to interpret and produce: Context diagrams Data flow diagrams (DFD) Systems flowcharts Planning a solution e.g. Gantt chart, journal/diary, report to management
Context DiagramsContext diagrams represent the entire systemas one process (circle) and show thesystem’s relationship with entities external tothe system (rectangles) and the data thatflows between them and the system (arrows)i.e. the system in context with users and othersystemsThe process circle is expanded into the firstlevel of a data flow diagram which may havemany process circles
Context Diagram Example - Budget Monitoring System QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.
Data Flow DiagramsDFDs show participants/external entities (rectangles),data (labeled flow arrows), storage (open-endedboxes) and processes (circles).They DO NOT show logic, media or interfaces‘data flow’ could be via paper, floppy disks, e-mail,computer circuitry, TV signal, etc. The media isirrelevantStudents find DFDs difficult to understand and moredifficult to create. Real, familiar examples are used toexplain them e.g. parts of the school library system
DFD Example - Budget Monitoring System QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.
Data Flow DiagramsStudents need to understand the DFD ‘rules’: A circle represents a single process that transforms input into output and must have at least one input and one output Data follows the arrows but is ‘moved’ via processes only Each process can be numbered and expanded into a detailed DFD of its own DFDs are not flowcharts - they don’t have a beginning or an end, there are no choices or branches indicated
Systems FlowchartsSystems flowcharts show media, storage,processes and order of flow betweenprocesses using a variety of standard graphicsymbols that need to be understoodThey DO NOT show data, interfaces orparticipantsMore hardware-oriented than algorithmflowcharts, showing types of input, output andstorage devices used etc, but similar to follow
Making DecisionsThe Analyst investigates possible solutions andreports to management Management decides on the preferred solution(s)and a report is prepared, including Feasibility study, covering Budget feasibility - is it affordable: costs v benefits? Technical feasibility - can it be done: is the IT available? Schedule feasibility - can it be done in the time-frame? Operational feasibility - will it fit in with organisational/user objectives? Analysis, including Gantt chart Organisational chart Design specifications to take into account concerns of users, management and participants
Gantt ChartsGantt charts show diagrammatically the time framefor the scheduling of tasks required to complete aprojectThey are used by Systems Analysts and ProjectLeaders as important planning toolsStudents find them fairly simple to read and constructif tasks are thoroughly itemised and in logical orderand the time scale is carefully constructedSoftware packages are available that construct chartsand link to a variety of related project managementtools e.g. MS Project
Organisational ChartShows top-down hierarchical structureof the proposed system’s personnelSimple - uses only rectangles andvertical or horizontal lines, one way inand one way out of each rectangle
Designing SolutionsAnalysts use a top-down approach i.e. breaka large problem into successively smaller,solvable ones that combine to provide asolution to the whole problemStudents too should consider the ‘big picture’e.g. fill in the system diagram (lecture 1) forthe proposed system to identify theenvironment, purpose, users, participants,data/information, IT (hardware and software)and how the information processes willoperate
Designing SolutionsThe same modeling tools that were used to representthe existing system can be used to represent theproposed system - context diagram, DFD, systemflowchartDesign could also include user interface design(screens, forms, etc) and involve screen/page designprinciplesA prototype approach could be used - develop aninitial, superficial solution and, with user input,customise and develop it into the final solution whichis more likely to please the usersTest data might be developed to verify the success orshortcomings of the final implementation
Implementing SolutionsInvolves installing the new system andtraining the participants/usersImplementation methods are Direct conversion Parallel conversion Phased conversion Pilot conversionMethods are easily understood with simpletime charts
Direct ConversionStop the old system, start the newe.g. the DET web services system (atthe school level)Fastest, least costly, most risky Old system New system Time
Parallel ConversionOperate both systems until new systemis perfected and takes overLess likely to lose data or stress staff onadoption but double the work and cost Old system New system Time
Phased ConversionNew system gradually takes oversystem functions while old system stillin operation for others and available for‘fall-back’ if unsuccessfulCan be confusing until completed New system Old system Time
Pilot ConversionNew system trialed and perfected on one partof the organisation then implementedcompany-wideProblems affect fewer people, old system stillavailable for fall-backe.g. Y10 On-line Computing Skills Test Old system New system Time
Implementing SolutionsThe advantages and disadvantages of eachimplementation method should be discussedStudents must be able to describe each method,compare and contrast methods and justify a selectedmethodThe underlined words above are key wordswith standard meanings across all subjectsand their exact interpretation must beunderstood by studentsi.e. drilled at every opportunity!
Social and Ethical IssuesInvolves machine-centred vs human-centredsystemsIncludes issues such as Changing nature of work e.g. deskilling, telecommuting (‘work from home’, ‘global village’), job satisfaction, human contact, e-commerce, Equity/inclusivity e.g. work for disabled OH&S e.g. ergonomics Employment, unemployment, training/retraining Ethics e.g. computer crime, breach of copyright, piracy, hacking, ‘identity theft’ Power and control e.g. the technological ‘haves and have-nots’