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					INTRODUCTION TO COMPUTER                                   LECTURE NO16

INFORMATION SYSTEM
       Information system consists of the rules and procedures establish to
deliver information to the people in an organization.

SYSTEM DEVELOPMENT OF LIFE CYCLE
    Creating an information system can be a complex task. It involves several
distinct phases, each of which often must be completed before a subsequent task
can begin. To help create successful information system, the System development
life cycle (SDLC) was developed. SDLC is an organized way to build an
information system. The SDLC is composed of series of five phases.
     Needs Analysis
     System Design
     Development
     Implementation
     Maintenance




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PREPARED BY M. ASIF NAEEM LECTURER IN BUITMS
INTRODUCTION TO COMPUTER                                     LECTURE NO16


  1. Needs Analysis
     During need analysis team focus on completing three tasks.
         i)      Defining the problem and deciding whether to proceed.
         ii)     Analyzing the current system in depth and developing possible
                 solutions to the problem
         iii)    Selecting the best solution and defining its functionality.
     Phase 1 is beginning when a need is identified for a new or modified
     system. Users may complain, for example, that the current system is
     difficult to use then a manager may approach the IS department,
     requesting a report that is not currently produced by the system.
              System analysts then begin a preliminary investigation, talking
     with users and the managers of the departments that are to be affected.
     The first important thing is to define the problem accurately. When a
     decision to proceed is made the system analyst must investigate the
     current system and its limitations. He works with people directly involve
     in current system. The knowledge gathered regarding the current system
     is documented in a number of different ways. Some analysts use data flow
     diagram, which shows the flow of data through the system. Other options
     are decision tree and structured English.




  2.      System Design
          During the second phase, system design, project team tackles the
       solutions. For example, a database application must be able to accept data
       from users and store it in a database. How many input screen are
       necessary, for example, and what will thy look like? What kind of menu
       options is there? What kind of database will the system use? The analyst
       and programmers involved at this point often use a combination of top-
       down and bottom-up design to answer these questions. In top-down
       design, the team start with the large picture and moves to the detail. They
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PREPARED BY M. ASIF NAEEM LECTURER IN BUITMS
INTRODUCTION TO COMPUTER                                     LECTURE NO16

       look at major functions that the system must provide and break these
       down into smaller and smaller activities. In bottom-up the team start with
       details and then move to big picture. Many teams, for example, use
       working models called prototypes to explore the look and feel of screens
       with users. They also use special software applications for creating these
       prototypes quickly. These applications fall in the category of computer
       aided software engineering (CASE) tool.

  3.      Development
             During the development phase, the programmers in the team are
             assigned to specific components of the over all system. If a
             component is being built, the programmers write the necessary
             code or use CASE tools to speed the development process.
             There are two alternative paths for the development. One is
             acquisition and other is local development path. If the team may
             realize that some or all of the necessary components are available
             then it will decide to acquire them rather than develop these
             components. Acquiring of the components means that the system
             can be built faster and cheaper than if every component must be
             developed from team. Another advantage of acquire components is
             that they have already been tested and proven reliable, although
             they may need to customize to fit into the overall information
             system.
             On the other hand if built in components are not available then
             team must have to be developed them locally. One important thing
             in this phase is that the team has to be developed a technical
             documentation. The technical documentation includes information
             about software features and programming, about the flow of data
             and processing through the system, and about the design and
             layout of the system. Testing is an integral part of this phase. The
             typical approach to testing is to move from the individual
             component out to the system as a whole. The team tests each
             component separately and then tests the components of the system
             with each other. Errors are corrected, the necessary changes made,
             and the tests are then run again.

  4.      Implementation
             In the implementation phase, the project team finishes buying any
             necessary hardware for the system users and then installs the
             hardware and software in the user environment.
             The process of moving from the old system to the new system is
             called conversion. IS professionals must handle this process

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PREPARED BY M. ASIF NAEEM LECTURER IN BUITMS
INTRODUCTION TO COMPUTER                                LECTURE NO16

        carefully, to avoid loosing or corrupting data. There are a number
        of different ways to convert a department or an organization,
        including the following.
        i)     Direct Conversion
               All users stop using the old system at the sane time and then
               begin using the new. The option is fats but it can be
               disruptive.
        ii)    Parallel Conversion
               User continues to use the old system while an increasing
               amount of data is processed through the new system. The
               output from the two systems is compared; if they agree
               switch is made. This option is useful for further live testing
               of the new system but it is fairly time intensive because both
               systems are operating at the same time.
        iii)   Phased Conversion
               Users start using the new system component by component.
               This option works only for systems that can be
               compartmentalized.
        iv)    Pilot Conversion
               Personnel in a single pilot site use the new system and then
               the entire organization makes the switch. Although this
               approach may takes more time than the other three, it gives
               support personnel the opportunity to test user response to
               the system thoroughly, and they will be better prepared
               when many people make the conversion.




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PREPARED BY M. ASIF NAEEM LECTURER IN BUITMS
INTRODUCTION TO COMPUTER                                 LECTURE NO16



  5.   Maintenance
         After the information systems are implemented, IS professionals
         continue to provide support during the maintenance phase.
         Changes, or upgrades to the system are made regularly during the
         remaining life span of the system. At some point, however, patch
         repairs to the system no longer meet user requirements, which may
         have changed radically since the system was installed. At this point
         SDLC has come full circle, and the analysis phase begins again.




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PREPARED BY M. ASIF NAEEM LECTURER IN BUITMS

				
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