2. System Development
Cycle
Planning, Design and Implementation represent the
main steps in what is in a number of courses - a
development cycle
In IPT it is the ‘system development cycle’ (which would
have been a better topic heading)
In SDD it is the ‘software development cycle’
It is basic problem-solving methodology:
Understand the problem
Plan/research/analyse/make decisions
Design a solution
Implement the solution
Test/evaluate/refine/maintain the solution
3. The IPT System Development Cycle (Grover)
Understand the problem
Outcome: Project plan
Make decisions
Outcome: Design option selected
Revision of system -
Design a solution cycle begins again
Outcome: New system created
Implement the solution
Outcome: New system is used
Test, evaluate and maintain the solution
4. System Development
Cycle
Keeping a system up-to-date and satisfactory is a continuous
cycle
Different texts have different interpretations of the way each
stage of ‘Planning, Design and Implementation’ is broken down
into sub-topics
I have used the syllabus here as the arbiter in the debate e.g.
analysis of the existing system is in the ‘understanding the
problem to be solved’ part of Planning, not in the ‘making
decisions’ part according to the syllabus but not according to
some other authors
If in doubt follow the syllabus and you can’t be accused of
getting it wrong! e.g. ‘Planning’ = ‘Understand the Problem’ +
‘Make Decisions’
Each course also has a set of tools used for
documenting/modeling
5. Modeling Tools
Modeling/documentation tools specified in both the IPT and
SDD syllabi are:
Data flow diagrams
Systems flowcharts
Storyboards
Data dictionaries
Gantt charts
Those in IPT only are
Decision tables
Decision trees
Block diagrams / Organisational charts / Hierarchical charts
Those in SDD only are
IPO
Structure charts
Algorithm flowcharts
6. Modeling Tools
Students need to know what each tool
is used for (and not used for) and at
which stage of the cycle it is appropriate
They are more likely to have to interpret
the resulting diagrams, charts, etc than
create them for complicated case
studies but can expect to do either for
simpler ones
7. Understand the Problem
Understanding the problem involves
Collecting data re problems with the existing system to
discover needs of users and participants.
Students must understand features, advantages and
disadvantages of:
Interview
Surveys/Questionnaires
Observation
Analysing the existing system (how, what, who) and
using modeling tools to represent it.
Students must be able to interpret and produce:
Context diagrams
Data flow diagrams (DFD)
Systems flowcharts
Planning a solution e.g. Gantt chart, journal/diary, report to
management
8. Context Diagrams
Context diagrams represent the entire system
as one process (circle) and show the
system’s relationship with entities external to
the system (rectangles) and the data that
flows between them and the system (arrows)
i.e. the system in context with users and other
systems
The process circle is expanded into the first
level of a data flow diagram which may have
many process circles
9. Context Diagram Example -
Budget Monitoring System
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
10. Data Flow Diagrams
DFDs show participants/external entities (rectangles),
data (labeled flow arrows), storage (open-ended
boxes) and processes (circles).
They DO NOT show logic, media or interfaces
‘data flow’ could be via paper, floppy disks, e-mail,
computer circuitry, TV signal, etc. The media is
irrelevant
Students find DFDs difficult to understand and more
difficult to create. Real, familiar examples are used to
explain them e.g. parts of the school library system
11. DFD Example - Budget Monitoring
System
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
12. Data Flow Diagrams
Students need to understand the DFD ‘rules’:
A circle represents a single process that
transforms input into output and must have at
least one input and one output
Data follows the arrows but is ‘moved’ via
processes only
Each process can be numbered and expanded
into a detailed DFD of its own
DFDs are not flowcharts - they don’t have a
beginning or an end, there are no choices or
branches indicated
13. Systems Flowcharts
Systems flowcharts show media, storage,
processes and order of flow between
processes using a variety of standard graphic
symbols that need to be understood
They DO NOT show data, interfaces or
participants
More hardware-oriented than algorithm
flowcharts, showing types of input, output and
storage devices used etc, but similar to follow
14. Making Decisions
The Analyst investigates possible solutions and
reports to management
Management decides on the preferred solution(s)
and a report is prepared, including
Feasibility study, covering
Budget feasibility - is it affordable: costs v benefits?
Technical feasibility - can it be done: is the IT available?
Schedule feasibility - can it be done in the time-frame?
Operational feasibility - will it fit in with organisational/user
objectives?
Analysis, including
Gantt chart
Organisational chart
Design specifications to take into account concerns of users,
management and participants
15. Gantt Charts
Gantt charts show diagrammatically the time frame
for the scheduling of tasks required to complete a
project
They are used by Systems Analysts and Project
Leaders as important planning tools
Students find them fairly simple to read and construct
if tasks are thoroughly itemised and in logical order
and the time scale is carefully constructed
Software packages are available that construct charts
and link to a variety of related project management
tools e.g. MS Project
16. Organisational Chart
Shows top-down hierarchical structure
of the proposed system’s personnel
Simple - uses only rectangles and
vertical or horizontal lines, one way in
and one way out of each rectangle
17. Designing Solutions
Analysts use a top-down approach i.e. break
a large problem into successively smaller,
solvable ones that combine to provide a
solution to the whole problem
Students too should consider the ‘big picture’
e.g. fill in the system diagram (lecture 1) for
the proposed system to identify the
environment, purpose, users, participants,
data/information, IT (hardware and software)
and how the information processes will
operate
18. Designing Solutions
The same modeling tools that were used to represent
the existing system can be used to represent the
proposed system - context diagram, DFD, system
flowchart
Design could also include user interface design
(screens, forms, etc) and involve screen/page design
principles
A prototype approach could be used - develop an
initial, superficial solution and, with user input,
customise and develop it into the final solution which
is more likely to please the users
Test data might be developed to verify the success or
shortcomings of the final implementation
19. Implementing Solutions
Involves installing the new system and
training the participants/users
Implementation methods are
Direct conversion
Parallel conversion
Phased conversion
Pilot conversion
Methods are easily understood with simple
time charts
20. Direct Conversion
Stop the old system, start the new
e.g. the DET web services system (at
the school level)
Fastest, least costly, most risky
Old system New system
Time
21. Parallel Conversion
Operate both systems until new system
is perfected and takes over
Less likely to lose data or stress staff on
adoption but double the work and cost
Old system
New system
Time
22. Phased Conversion
New system gradually takes over
system functions while old system still
in operation for others and available for
‘fall-back’ if unsuccessful
Can be confusing until completed
New system
Old system
Time
23. Pilot Conversion
New system trialed and perfected on one part
of the organisation then implemented
company-wide
Problems affect fewer people, old system still
available for fall-back
e.g. Y10 On-line Computing Skills Test
Old system
New system
Time
24. Implementing Solutions
The advantages and disadvantages of each
implementation method should be discussed
Students must be able to describe each method,
compare and contrast methods and justify a selected
method
The underlined words above are key words
with standard meanings across all subjects
and their exact interpretation must be
understood by students
i.e. drilled at every opportunity!
25. Social and Ethical Issues
Involves machine-centred vs human-centred
systems
Includes issues such as
Changing nature of work e.g. deskilling, telecommuting
(‘work from home’, ‘global village’), job satisfaction,
human contact, e-commerce,
Equity/inclusivity e.g. work for disabled
OH&S e.g. ergonomics
Employment, unemployment, training/retraining
Ethics e.g. computer crime, breach of copyright, piracy,
hacking, ‘identity theft’
Power and control e.g. the technological ‘haves and
have-nots’
