The Systems Life Cycle: Design

The Systems Life Cycle: Design

Designing the new system

So far, our analyst has….

Collected information on how the current system works

Established inputs, processes & outputs

Recorded information Identified problems Identified suitable hardware

& software Identified user & information

requirements

In this next stage, the following are designed: Inputs to the system Outputs from the system Files/databases needed to store the

data The processing required to produce

the outputs Any validation required The data needed to test the system

Designing data collection forms/screen layouts

DCFs can be paper based or on screen

Need to take great care – why? Easy for workers to fill Easy for secretary to read Eg one box per character Minimise errors Requirements must be clear Design may depend on user

requirements/required output

Designing screen layouts

Screens must be easy to use

Attractive to look at Limit possible errors Guidelines Navigation Input devices

Designing report layouts Influenced by views of user Also by user requirements Attractive Not over-elaborate Instructions for navigation Output format

(graphs/lists/reports/tables)

Medium (paper/screen/sound)

Designing report layouts Layout: who sees it? –

users and customers, so need to consult with Company

Easy to read Professional Style: house style 3 or 4 different designs

for approval

Designing screen displays Keep simple &

consistent Not over-elaborate Attractive Navigation Users: no need for

advertising Instructions for use

Designing data & file structures Master files Transaction files Field names Field types Field lengths Validation rules Field descriptions Key field Relationships Test plan

Designing validation routines As many data

validation routines as possible – why?

Range checks/length checks/presence checks/format check/

Designing other ways of reducing errors Reducing volume

of input data (coding)

Direct data entry methods

Specifying the required HW & SW Final stage Earlier: general

recommendations Now: specific

May include supplier details

Volume of data may determine input/output devices

Storage: indexed sequential or sequential?

Software: Build or Buy?

Off the shelf or Purpose built

Off the shelf

Advantages: Mass produced so

cheaper Available straight

away Rigorously tested Helplines etc

available

Disadvantages: Cannot be

adapted/difficult to adapt

May have distracting extra features (eg Office Paperclip)

May not match existing system & software

Purpose built

Advantages: Designed

specifically for the task

Does not need to be adapted

Programmers can make any required changes

Disadvantages: Cost Testing limited

to perception of programmer

Support limited to team of programmers

Time to develop