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    Systems Lifecycle workbook Systems Lifecycle workbook Document Transcript

    • Systems Life Cycle – Applied ICT AS /A2 -2- THE SYSTEMS LIFE CYCLEThe SYSTEMS LIFE CYCLE is a term used to describe the stages in an IT project.These are: • Analysis • Design • Development & Testing • Implementation • Documentation • Evaluation. The term life cycle is used. This is because the process never ends. Systems are created, they become mature, they grow old and are replaced by new ones.Why a new system?1. The current system may no longer be suitable for its purpose.•Changes in the way of work is carried out means the system is no longersuitable.•Starting out with only ten staff a few short years ago, the system could easilycope with the workload. But now there are a thousand staff members in manyoffices around the world. The system just cant cope.•External influences. For example, new regulations have come along which insistthat certain records are kept for years. The existing system was never designedfor this.2. Technological developments may have made the current system redundant or outdated.•Competitors are using more advanced systems that perhaps reduce their costscompared to yours, thus placing the company at a disadvantage.•Customers use more modern systems and insist that you upgrade yours to allowfor easier data transfer.•The software supplier has warned that the version you are using will no longerbe supported after next year. You have to plan for change.3. The current system may be too inflexible or expensive to maintain.Why is SLC (systems life cycle) needed?IT change is particularly risky!What could have been done better?
    • Systems Life Cycle – Applied ICT AS /A2 -3- What could reduce the chances of failure? As people have learnt from past mistakes, a model has to be developed and refined over the years to try and maximise the chances of a successful project. This method /model is called the SYSTEMS LIFE CYCLE. It consists of a series of stages that take a project from its very first stages to the final outcome of a fully working, fully integrated system. Systems Development Life Cycle Preliminary Investigation Problem Definition Implementati on Training Conversion Analysis Ongoing Activities Evaluation Gather data Project Management Maintenance Analyze data Feasibility Assessment Documentation Develop Information Gathering. requirements Development Scheduling Programming Design Testing Preliminary design Detail design 4a-ANALYSIS (stage 1) [identifying and investigating] •1A-The different methods of researching (fact finding) about a situation are:- Observation: the point of observation is to see who does what in an organisation and what information they do it with. By simply watching people working is also fairly straightforward to watch how data flows around a system. Observers have to be careful of the Hawthorne effect. This is where workers modify their behaviour because they
    • Systems Life Cycle – Applied ICT AS /A2 -4- know they are being watched. The aim of observation is to find out what actually happens, not what the workers think observers expect to see.- Examination of docs: All documents which are used within a system need to be examined. These will be eventually duplicated or replaced with alternative versions or even discarded in the new system. The types of document which need to be examined are – Data capture forms, system documentation, business reports, invoices, bills, letters etc.- Questionnaires: The use of questionnaires is a very popular method of fact finding. A great deal of time is spent on preparing questionnaires in order that the right type of question is asked in order that the most relevant information is gathered.- Interviews: This method is used in some form in gathering information in every situation. A great deal of time and energy is spent on producing the most appropriate ‘script’ or lists of questions. An interview can take more time to organise and it is extremely difficult to repeat so it is vital that the questions asked are the right ones. The following things have to be kept in mind for a successful interview:  determine the people to interview  establish objectives for the interview  prepare for the interview  conduct the interview  document the interview  evaluate the interview  causes for unsuccessful interviews. • 1B- Establishing the inputs, outputs and processing in the existing system: After all the fact finding methods have been completed and the results are collated, the next stage is to use these to define all the inputs, outputs and processes which are employed in the existing system. A system can be defined by using the definition of desired outputs to understand what inputs are necessary. The following questions can be used for this method: 1. What essential outputs must the existing system produce in order to satisfy the system users’ requirements? 2. What transformations are necessary to produce these outputs? 3. What inputs are necessary for these transformations to produce the desired outputs? 4. What types of information does the system need to retain? 5. How to identify the sources and volume of input data and collection methods?
    • Systems Life Cycle – Applied ICT AS /A2 -5- For reference goto: Outputs#Systems_Defined Identify the sources and volume of input data and collectionmethods. By examining all the documents, this will enable the systems analyst to identify the documents which are currently being used to input data to the existing system. Observation will enable the systems analyst to determine the frequency of the addition and/or deletion of records. Identify manual and computer procedures necessary to achieve the current output.•1C- Recording information about the current system:It follows that there is a need for recording the facts since keeping accuraterecords is essential. The basic rule is to write them down. The following aresome guidelines for good documentation: • The first is that information must be recorded as soon as possible. • The simplest recording method should be used and the work must be understandable. • Documentation material must be organised. The best way of doing this is by using data flow diagrams. Most systemsdeal with information in one way or another. What really matters is how theinformation flows through the system. How does it branch and re-join. Whatoutputs are created and so on.The data flow diagram seeks to show this movement through thesystem.DFD is agraphical representation of the flow of data through an implementationsystem It is common practice for a designer to draw a contxt-level DFD firstwhich shows the interaction between the system and outside entities. Top DFDwould have components 1 2 3 4 5, the subcomponent DFD of component 3would have component 3.1, 3.2, 3.4, 3.4.etcLevel-0 is the context diagram (concerning the current system).
    • Systems Life Cycle – Applied ICT AS /A2 -6- Data Flow Diagram Set Level-0 DFD Context Diagram Level-1 DFDs .... Level-n DFDs .... .... 10/21/99 Primitive DFDs 1Level-1 is the current system.
    • Systems Life Cycle – Applied ICT AS /A2 -7-* You should just know these two types of DFD and explain theirrelevance for recording information about the current system in aworkplace scenario.System flowchartsThese show the relationships between the various systemsin the company (or even outside if relevant) - how theyinteract, what depends on what and so on.1D- Identifying problems with the current system - The Problemdefinition phase: In this stage, it is analysed that what are theproblems or limitations of the current system. This may be done through:ObservationExamination of documentsInterviewing employees about their issues with the current system (alsothrough questionnaires)Analysing the total costs of the current systemChecking the performance of the existing system.(After having analysed the current system, its processing, its drawbacks, nowthe new system to be created is analysed)1E- Identifying suitable hardware and software for a new systemAnalysing required outputs, storage and processing requirements using the DFDswill allow the Systems Analyst to make generalised recommendations forthe software and hardware.1F- Identifying the user and information requirementsBy merging the interviews, answered questionnaires, and the investigationdocuments, the system analyst will be able to identify what the users (in aworkplace) require from a new system and what information will thenew system require. This is also known as a ‘report to management’which:
    • Systems Life Cycle – Applied ICT AS /A2 -8- 1. Summarizes the problems found in the current system 2. Describes the user and information requirements for the new system 3. Makes a recommendation about what to do next (includes a cost-benefit analysis)4b- Design (stage2)Now that the project manager and the client have agreed on the basicrequirements, it is time to define how the project is going to be carried out. Thisis the Design phase.2A- Specifying the required hardware and softwareHardware configuration includes deciding on the type of computer, whether tonetwork them, peripheral devices and storage devices.A company has to decide which software(s) to use. Someone could be hired towrite one or maybe a software package maybe bought from the market.For example, a project planning company may have certain software andhardware requirements, such as project management software, Gantt chartsoftware, planning software, high resolution printers, graph plotters, expensivepointers, etc. The company may also require high storage capacity; therefore storage devices and backup devices will be listed too in this stage. Therefore, the system planners will make a list. The volume of data to be stored and the data to be printed or displayed affects the choice of storage devices and output devices. 2B- Designing data collection forms, screen layouts
    • Systems Life Cycle – Applied ICT AS /A2 -9-Here is a data collection form, staff members fill these forms and then theinformation given on these forms are input in the database of the new system.So, these forms will be designed in such a way that they are easy to fill in andthe staff does not face any confusion.This is a screen layout. The systems planners will design such a screen layout,which is easy to understand and use, does not use too dark or too bright colours and the overlapping of windows is also allowed for multi-tasking. Both of these will be designed according to the database requirements and the system’s requirements.2C- Designing report layoutsand screen displaysReport layoutsThese will depend upon thesystem’s users’ requirements.Whatever the sort of contentand presentation he wants, thereport layouts will be designed insuch a way.
    • Systems Life Cycle – Applied ICT AS /A2 - 10 -Screen displaysThe users will list the sort ofscreen displays that they will liketo work with. Some may want abrighter display, some may askfor a dull one, therefore such adisplay will be designed whichwill satisfy all users.2D- Designing validationroutines•Data preparation involvesgetting the raw data into a form that can be processed by the computer.Verification and validation are included in data preparation.•Verification makes sure that, if a keyboard is being used, no typing mistakeshave been made.•Various validation methods can be used to trap some of the errors. Rememberthat a computer program performs validation.•Codes can also be used to save typing time, reducing storage space and thesecodes can then easily be checked for errors (validation).2E- Designing the required data/file structures & programmingspecification
    • Systems Life Cycle – Applied ICT AS /A2 - 11 -•The data structures and programming will depend on the types of processingand input and output structures.•How will files be organised? (File structure) - Serial access, sequential access or random access?•What about the database design? - Table structure & data relationshipsProgrammingspecificationsThis shows adiagram of asystem planner whowill make use of thedata entered, theprocessing and theoutput, and thenwill make aprogram accordingto it.4c- Development & testing (stage 3)Now that the client has agreed on what needs to be done, and the Analyst hasdefined precisely what needs to be done - it is time for the project to be actuallydeveloped.The development stage is about taking the design forward and putting it intopractice.
    • Systems Life Cycle – Applied ICT AS /A2 - 12 -3A- Creating data structures, program modulesNow the system analyst actually creates the file and data structures that he haddesigned in the previous stage.He also now starts to program according to the programming needs he hadlisted in the previous stage.He will use logic flowcharts and pseudocode to facilitate code development andprogramming.3B- Testing strategiesEach module will need to be tested with different types of test data.Types of test data to be used are:Testing each module with normal data - data which is acceptable and willnot generate error messages.Testing each module with live data - data which is already being used in theexisting system.Testing each module with abnormal data – data which is outside acceptableranges or is of the wrong data type.Testing each module with extreme data – data which is at the extremeboundaries of a range.The system will also need to be tested as a whole.•All the above kinds of data are input in the system to test it.•The system is tested with data that contains no errors to see if it produces thecorrect results (normal/live data).•Then, known errors are introduced to the new system to see how the computerreacts and processes the incorrect data (abnormal data).•Then it is checked if huge amounts of data can be processed or not.•Extreme data is entered to check if the validation routines are working or not.3C- ImprovementsPrior to the implementation any improvements which might be needed are madeto the system in the light of the testing of the system. These could be amendeddata structures or even amended program modules.If there are any errors or slow processing or any programming mistakes orlimitations, these are all amended.
    • Systems Life Cycle – Applied ICT AS /A2 - 13 -If all goes well, we move onto the next stage of implementation.4d- Implementation (stage 4)This is an interesting time.... the implementation stage has been reached.The system has been developed and tested. It is working correctly and doingeverything that was agreed during the design stage. The business is waiting ineager anticipation for the new system to be handed over to themIdentifying the different methods of system implementationHow does a company implement a new system really depends on its size.Solutions range from a microcomputer or two, to a system that uses a number ofnetworked PCs or even a system based on large computers.Systems may be introduced into an organization in three ways: 1. Parallel running: The existing system and the new system are run together until there are no mistakes with the new one. o If the new system fails, then because the old system is still there, the old system can be used until the problem of the new system have been sorted out. o Parallel running provides an ideal opportunity to compare the results from the new system with those of the old system. o However, it has a drawback that since each job is done twice, there is much more work for users. 2. Direct changeover: in this system, the users decide to start using the new system on a given date. Basically the existing system is replaced by the new one without any ‘running in’ period. o This method is only used for small computer systems since in larger ones problems reveal themselves during the first month and the result can be a havoc. o The number of staff needs to be less and trained too. 3. Phased implementation: This is parallel running on a small scale only part of the system is introduced to run alongside the existing system. When that works the next part or phase of the system is introduced. The existing system is gradually replaced by the new system. Each job is
    • Systems Life Cycle – Applied ICT AS /A2 - 14 - introduced separately rather than all jobs being introduced in one go. o Similar to parallel running except only part of the system is run in parallel o Limited size direct changeovers o System is installed gradually o Gives the opportunity of valuable feedback while the system is being developed. o Takes some of the pressure off the developer - small parts of the system are delivered before the whole system is completed 4. Pilot running: The new system is operated in one area of the organisation only until it is working properly and then another area has it introduced. The entire system is used by a designated set of users. o The system is run initially in one functional area only o The advantages and disadvantages of pilot running are a combination of those for direct changeover and parallel running.4e- Documentation (stage 5)5A- Technical Documentation-Technical documentation is used to explain a system to a specialist, either aprogrammer or a systems analyst. Since these people understand computerterminology, this guide need not be as simple as the user guide.
    • Systems Life Cycle – Applied ICT AS /A2 - 15 --This documentation is extremely important since someone new to the projectmight use it and there may be no one around who was involved with the originalproject.-This documentation will be needed later when the system is to be improved orupgraded.Technical documentation has two sub-documentations. Developing systemsdocumentation consists: Results of analysis stage Description of the system What is expected of the system System’s design’s specifications Screen layouts Test plan Test data This document is basically concerned about the system’s life cycle’s various stages.The other sort of technical documentation is the developing programdocumentation, which consists: Software used Description of the software used Purpose of the software Data capture forms’ format Output Flowcharts Program listing Notes to assist future modifications5B- User documentation:-A guide to simple elements of use of the software and hardware making up thesystem.-This documentation or guide is prepared so that a user can turn to it forlearning a new procedure or for dealing with a problem that has arisen.-Users are usually non-technical; therefore any specialist or technical languageshould be avoided.User documentation will consist:-Minimum system requirements-Login and logout procedure and access to system, save arrangements
    • Systems Life Cycle – Applied ICT AS /A2 - 16 --Brief explanation of menu system-Querying and finding information-Data entering, updating and deleting procedure including - display screens etc-Printing information including invoices, reports etc-Backup and security-Operating system information, error detection and corrections and on-line help/procedure.-Meaning of error messages4f- Evaluation (stage 6)The implementation stage is over: The system is up and running, staff is fullytrained and bugs have been ironed out.This new stage is called the Evaluation phaseIt is at this point two key questions are considered: Does the finished solution meet its requirements? Does it solve the problem?For example:Analysis states that the system should be able read the data file in less than 3seconds.Question: Does the system meet this specification?Answer: Yes, the data file is read in 2.8 seconds.Evaluating a new system in terms of the efficiency, ease of use andappropriateness of the solutionThe new system is evaluated in terms of:*Efficiency*Ease of use*Appropriateness*Closeness to the expected solutionThe new system may be evaluated by:
    • Systems Life Cycle – Applied ICT AS /A2 - 17 -  The analyst and someone from the organization  An independent third partyThe new system will be evaluated by: Using test results. A comparison has to be made of the actual results together with the expected results. If the results are not as expected, refinements may be needed. Asking the users of the system. They will be able to tell if a system does have what they originally wanted or if there are any improvements needed? Checking if the objectives and criteria listed beforehand are being met.The results of evaluation are used to identify limitations of the newsystem.Using these limitations, improvements can be made to the new systemfor ease of use and its appropriateness in usage.Maintenance- maintaining the new system is a never-ending process and canbe done by:-Enhancements to the system.-Fix bugs and problems in the system as soon as they are identified.For a better understanding, please And view the whole presentation.References:1. www.teach-ict.com2. www.wikipedia.org3. Life cycle [1] presentation by Ritchie King c/o www.teach-ict.com5. “Information systems for you” by Stephen Doyle6.