The Systems Life Cycle Stages of the life

The Systems Life Cycle

Stages of the life cycle n Exact definitions vary, but the main stages of the life cycle are:

Waterfall & Spiral n 2 key methodologies of the system life cycle n. What are the differences?

Information gathering n Interview: This can be time-consuming, but it does allow you to probe for answers and get first-hand information. n Questionnaire: This is useful when there are lots of users, although there is a limit to how much you will find out. n Observe the current system: Although timeconsuming, this is objective rather than subjective and you might spot things that the user doesn’t. n Examine the existing documentation: This is very useful for identifying the data requirements, as well as the input and output required.

Feasibility study n A feasibility study is a report to identify the possible solutions to the problem and how ‘possible’ they are. n Technical, Economics, Legal, Social feasibility of the new system. n A typical feasibility study would look at the following options: – Should we: Stick with the old system? Adapt the old system? Create a new computerised system? – Should we: Buy an off-the-shelf package? Employ a programmer to create bespoke software? Write it in-house? – Could new system be developed in the required time?

Key Factors in a Feasibility Study n Technical – Is the HW/SW available to solve this problem? n Economic – Is the proposed solution cost effective n Social – Impact on jobs, skills, training of staff

Importance of Analysis n Problem must be accurately defined to solve it effectively n User may not understand potential of computer systems n Developer not likely to understand the industry which the user is working in n Developer must produce a solution/software that the user requires to meet their needs n Clear communication between user and developer is important

Requirements Specification Contains… – Input requirements – Processing requirements – Output requirements – Clients agreement to requirements (signed) – What Hardware will be needed to run new system

If problem is not defined accurately at the beginning…. n Client will be unhappy n Software will be useless. . . n Programmer will not get paid!

Design n. How will the system be produced? n. HCI n. Pseudo Code n. Database Design – Fields – Records

Design Specification Used by programmers to ensure they are producing the correct system n Input design n Output design n Data structure n Pseudo Code algorithms/flowcharts n Data flow diagrams n Entity Relationships Diagram n Sitemaps

Implementation n. Programming!

Installation Strategy n Method of implementation – parallel/pilot/phased/direct n Training program must be devised n Hardware must be purchased and installed n System must be tested with real data by end users n Write technical and user documentation

Test Data n. Normal n. Extreme n. Erroneous 5 10 No Enter Number between 1 and 10

Documentation n User Manual – Written from the users point of view on how to use the system n Technical Documentation – Variable Names, Data Structure, how the code works, Procedures. DFDs, Flowcharts, Entity Relationship Diagrams. Meant for future programmers.

User Manual n Contents of user manual usually include… – Installation instructions – Minimum required hardware specifications – Input /Output procedures – How to operate the system – Backing up and archiving procedures – Error messages/trouble shooting – FAQs

Technical Documentation n Written for future programmers. n Contains – Variable Names – Data Structure – how the code works – Procedures names – DFDs – Flowcharts – Entity Relationship Diagrams.

Data Flow Diagram (DFD) n This is a diagrammatical way of showing how data moves around a system. n It is not concerned with how the system processes the data – it just shows the flows. n It uses four symbols:

DFD example n The following is a DFD for a meter reading:

Evaluation n End User Requirements decided on in Analysis n Does it meet them? n Future Enhancements n Important to user because need to be sure software performs as required – is it actually what they wanted? ! n Important to developer because it determines the end of the job if they are being paid for producing a suitable solution

Software Maintenance n Once software is completed it needs to be maintained/upgraded as its requirements change n Corrective Maintenance – To correct bugs found in software when being used n Adaptive Maintenance – To alter software because of external need eg VAT paid changes from 17. 5% to 15% n Perfective Maintenance – To improve performance of software