System Life Cycle

An overview of the softwareIncludes input and output methods and backing storage.This will be accomplish by system flowcharts.A web site might require a site map.A detailed description of the way the software worksAlgorithms and formulae usedThe program source code with commentsSoftware is produced as a set of small components or modules.Spreadsheet solutions need details of the formulae and macro used.

Descriptions of record, file and other data structuredata tables and relationships between themKey fieldIndexed and queriesdocumentationProducing guidance about how the system works, or how to use it, for the people who will have contact with it.evaluationChecking how well the system performs all the tasks it was designed to carry outUser documentationError messages and correctionThere will be explanations of common errors and how to recover from themUser documentationTutorialA step-by step tutorial is provided, with sample data so that users can learn the software in a systematic wayUser documentationBacking upThe documentation should include how to make backup of the data so that recovery from accidental data loss is possiblemaintenanceChanging the system to fix problems, adapt to changing requirements and add improvementsProblem definitionAlways involves a compromise between the people in the organization and the system analystPeople in the organization know how their business works, what the nature of the problem is and how much they can spendthe analyst know about computer and what is possibleProblem definitionFirst the analyst is told what is wantedHe/she produces a report that states what is possibleThis is called the feasibility studyIf the feasibility study is accepted, then the analyst needs to find out as much as possible about the organization and the problem to solved.This lead to the collection of informationCollection of informationObservationInterviewQuestionnairesDocument collectioninterviewsPro: the best way of finding things out because the questions do not have to be fixed in advance; the analyst can change them according to the answers the interviewees giveCon: is that interviewing takes a lot of timeRecording dataData collection methods outlined above will provide a large amount of data about the present systemThis raw data needs to be collected and studies so that is can be turned into useful informationThe best way to deal with information like this is probably to record it in a diagram data flow diagram or flowchart DesignThe new system must now be designed to meet the requirement specificationIt is often useful to break down a large system into subsystems that are easier to work withDesignSupermarket information system Customer sectionBanking sectionStock control

DesignA structure diagram can be produced to show how subsystem fit together to make the whole systemDesign stageIt is very important to think about the way each part of the system interacts with its users.This human user interface must be consistent throughout the systemThe following points might be considered:Design stageHere are some of the decisions that are taken during the design phaseThe screen layout is designedThe error messages are writtenThe way that you will navigate from one page to another is definedThe menu buttons are chosenThe font style, size and colour are pickedHow data will be dealt with is specifiedWhat documents can be printed outThe hardware will be neededDesign stageUse of colourSoundFlashing symbolsLocation of item on the screenMovement from screen to screenMaking choicesAppropriate use of language

Use of colourColour useful to highlight messages, but too many colours can be confusingGood contrast between colours so that words are readable and images clear.red warning colourSome user may be colour blind avoid combining red and green, blue and yellowsoundSound should be reserved for situation where it is essentialIt would be a distraction to use sound in accounts systemWarning sounds can be usedBarcode reader in the supermarkets bleep to indicate correct reading

Flashing symbolsUse to attract user attention

Location of items on the screenKeep the same items in the same place on all screens forming part of the systemThis will make the system easier to useUser tend to look mostly at the top third of a screen important messages may not be seen if they are placed at the bottom of a screen

Movement from screen to screenThe same method is always used to move between screens

Making choicesThe same method is always used to indicate that they have made a choiceThe input device used is likely to be the mouse or the keyboard, but should not be a mixture of the two

Appropriate use a languageThe type of language used is suitable for the users of the systemGraphics may work better than words in some casesOutput designsAll computer system consists of InputProcessOutputstorageOutput designsAs outputs of a system often affect how the system functions, outputs are usually examined first.Outputs can take many forms and may include:An invoice, receipt or billA screen displayA sounddesignTo decide what the output should look likeExample:The organization is a mail order company and the analyst has been asked to produce a system that will allow the telephone receptionists to takes orders over the phone.The company bosses are only concerned with whether the people on the phones can search to see if stock is available and then place an order.They are not interested in how the system does.

designThe analysis will design what the output screen will look like and then produce what is known as a prototypeIt wont work yet because no processing has ben designedManagement and worker will actually use it to be able to tell whether it will be able to do all the things that they want it to do.

outputThe Golden Rule is to be user-friendly. This mean that the output must be appropriate for the needs of the audience.Users should only be shown the information that they need and it should be communicated in a way they will easily understand. Layout is an important as content

outputThe layout of output screens and printout should first be sketched in roughThey should then be shown to the user to check they are OK.

Input designOnce the type of output has been established the type and method of capturing the data needs to be considered.Inputs can consists of:Numerical data, PicturesSoundstextDesign input screens that will produce all the data the system needs

Input designOnce the decisions has been taken about the data that in required, the analyst has to decide how that the data can be collected and what sort of data input should be usedWill automatic data collection is used?A sensor telling the system when someone enters a buildingAre questionnaires going to be used?

Is the data going to be input by someone using a keyboard and screen?

Input- how the data is captureThe input data might needed to be organized into field of fixed or variable lengthThe use of codes can reduce the file size.Screen form should be sketched showing what the user will see whilst they input the dataData storageHow much the data needs to be stored?Will the amount of data that needs to be stored increase in the future, as the needs of the organization change? By how much?How often are the different data items going to be accessed?Who should have access to the data and how will that access be controlled?What sort of hardware is going to be needed for the storage?When the data is input to the system, it will have to be checked to make sure that it is accurate.Special routines called validation routines are set up to do this.Exercise (design stage)Give three types of diagram which could be produced in carrying out the design of a new system.

Development/testingConstruction of new system includes:Writing any new programsSystem testing and debuggingA system is tested both during building and after its built.You need to know what tests are done and whytestingIt is important that a new system is thoroughly tested before it is introduced.Testing is carried out regularly throughout implementation of a systemThe general principle of testing is to check that the system works properly with typical data, data at the limits of what is allowed (extreme data), and data that is wrongIf the result s of all tests are positive, the system can be introduced, or implemented TestingTests are carried out to see if the design has worked When a system is tested, they are five stages normally followed:1: the system is tested with data that contains no errors to see if it produces the correct results.(normal test data)Normal data anything that the programmer knows should work in the system

testing2: It is tested with data that contains errors to see how this data will be processed.It will be impossible for the computer to detect every type of error.Invalid data anything programmer knows that the system should reject

testing3: the system is tested with very large volumes of data to see if it can handle this, And if it might be able to cope with increased work n futuretesting4: system processes that are required only occasionally are then tested.Finally, data that is known to be close to or outside the range of the system is entered to see how this is processed The range checks included in the validation program should detect any unsuitable data.TestingAny part of the system that doesnt work is said to have a bugProgrammer know which parts of the system need to be debuggedAcceptance testing checks whether or not the system meets the needs of the intended users.Might involve a trial run with real users operating the systemExercise(Design)Describe five improvements which could be made to this screen.

Exercise (Testing)The new system will be tested. The month part of the data of birth field must be a whole number between 1 and 12 inclusive. Using this as an example, describe the following three types of test data.Abnormal dataNormal dataExtreme dataImplementationThe hardware and software that have been selected are installed in their working positions, and set to produce the required outputsThere are three common ways of installing systems in organizationsDirect implementationPhased implementationParallel implementationDirect implementation Used only where a small system is being implemented.All the user begin to use the system on a certain dateThe method is quick and simple where no problem occurDirect implementation It is not suitable for larger systems because, despite testing, problems do often occur in the early stages of implementation And if all users tried to switch at the same time, there could be chaos.Advantage: benefits of the new system happen as quickly as possibleDisadvantage: any bugs not picked up during testing could have disastrous effects.Phased implementationThis method introduces each task separately and ensures that it is running smoothly before another task is brought into the systemExample: in the supermarket, the stock control section might be implemented first.Advantage: the new system have time to be fully tested so fewer problems should occur.Disadvantages: take a long time to introduce the new system so the benefits take a long time to come throughParallel runningIn this method the new system is started and run alongside the old systemWhich can act as a backup if problem develop with the new systemResults from the new system can be compared with results from the old systemAdvantage: new system can be tested very quickly and problems can be sorted out without important operations being affectedDisadvantage: all tasks need to be done twiceDocumentationWhen software is written, the job of the developer does not end there.The purchase of software wants to know how get the best out of it.User documentation is provided to help.Technical documentation is needed to help programmers who work on the software in the future.

DocumentationWhat is the user documentationWhat the software doesInstructions for installing and running the softwareSystem requirementInstructions about preparing and entering dataUnderstanding the output dataError messages and correctionTutorialBacking up

User documentationIllustrations may be used to help explanationsGuide may include examples and exercises to help users become familiar with the new systemShould have a contents page and index to help users find the answers to their questionsGlossary that explains any new terms may be usefulTechnical DocumentationTechnical documentationMost software is complex and written by teams of people. It changes often. It is unlikely that the same people who wrote it will maintain itPeople responsible for maintaining the system do need to know how the system works, and may have to adapt the system as user needs change

Technical DocumentationTechnical documentation should include:An overview of the softwareA detailed description of the way the software worksDescription of record, file and other data structuresDetails of all screens and reportsTesting and test plansDocumentation exerciseGive one disadvantage of a paper-based user manual.Why might a software producer want to supply user documentation on a web site?

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What sort of diagram is used to shoe the relationship between processes, files, input and output?What is data flow diagram used for?What does a program flow chart represent?What is a pseudocode?What type of flow chart looks in detail at how a process works?

EvaluationMonitoringNo computer system is perfectA new system is monitored throughout its life, most particularly in the early stages.There will be faults that do not show up until later,When lots of data is entered, or unusual situations ariseOnce the system is installed its performance will be monitored to see whether its working properly.From time to time itll be evaluatedThis is a check to see if the system still meets its objectivesEvaluationBasically repeating the research carried out at the start of the systems life cycle.In other words observing and interviewing users and studying printouts.

EvaluationQuestions are asked such as:Has the software any shortcomings?What improvement may be made in the future?Does the software work as is desirable?Was the documentation adequate?Is there on-screen help?Does the software give helpful feedback of operator errors occur?

EvaluationThe best way for developers to do evaluation is by consultation with the client.It can be helpful to follow some of the same methods which were used in the investigation phase such as:QuestionnairesVisit and interviewsEvaluationIt is good idea to keep this cycle of consultation and development going in order to ensure that the software remains as effective as possible.MaintenanceIs the process of updating and refining software throughout its lifeMaintenance is made easier ifThe original software is constructed in a logical and ordered wayModules are kept smallThe programming style is kept simpleMaintenanceProgram faultsIt is lucky if a program does not have a few remaining bugs after it has been delivered.With a big program, it is extremely difficult to test Program flow chartsThe steps taken by program to carry out a process are called algorithm.Algorithm can be expressed as a flow chart