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Posts tagged ‘SDLC’


System development life cycle

There are two types of SDLC the 4 stage and the 6 stage

Note that in the six stage SDLC some of the steps fit into the four stage

4 stage





6 stage

1.Prelimenary investigation






A system has an SDLC which uses different methodologies such as waterfall, rad, prototype or o-o, it is made in three phases

Phase one – The initial investagation

  • Feasibility study
  • Estimate
  • Roles/ organisation chart
  • Scope
  • Recommendations

Phase two – Requirement modelling

  • Data flow diagram (DFD)
  • o-o Modelling (using the case diagram)

Phase three – Design

  • System design specification

What is a system?

Input –> Process –> Output –> Feedback (continuous loop)

Input– Anything that goes into the system

Process– The process that results in the output

Output– The result of the process

Feedback– Information from the previous cycle used to change the process in proceeding cycles

System enviroment

system boundary- defined by the rules placed on the particular system, often difficult to define the exact boundaries of a system

input- Only occurs in open systems, any information that is put into a process

output- The result from the process

feedback- Information gathered from an output used to change the way/choices the system makes the next time it runs.

control- ???

May also have

Emergent properties-

Interfaces to other systems-

Sub-systems- Systems that operate separately from the main system

Different processes

Online– The application receives instructions and completes them eg. when surfing the net

Real time– The application needs to respond to requests in a certain amount of time, usually seconds eg. airplane controls

Batched– The application saves the requests and processes them at an off-peak time eg. overnight banking

Different systems

Open system– A system with input, it changes its behavior according to conditions outside its boundary

Closed system– A system with no input, it doesn’t interact with the enviroment

SDLC– System/software development life cycle, the process used to develop/upkeep a system/software

Cause and effect

One point of reference changing will cause a chain reaction where the system reshuffles to make everything work

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