Post on 24-Feb-2016
description
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