The Software Development
Process
Systems analysis
Systems design
Implementation
Testing
Documentation
Evaluation
Maintenance
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Systems Analysis
What is a systems analyst?
 A systems analyst observes, clarifies
and models an existing system to
assess its suitability for
computerisation. In the process, the
analyst could also find ways of
improving the system.
 The systems analyst must have a
sound technical background. They
may once have been programmers.
2
Skills and techniques of
the Systems Analyst
The systems analyst must
extract the clients needs
document these needs in a formal
way
communicate these to
the designers
3
Extracting the Clients
Needs
Extracting the clients needs is known as
requirements elicitation.
This is done by:
 Interviewing the client’s management personnel
 Making observation notes of the client’s business
 The analyst will also inspect information sources
used by the client to keep track of their business.
From this the Software Specification is created. This is
a legal binding document between client and sw company
4
The Requirements
Specification


is the end result of the
requirements elicitation
is a written statement of what the
design team must go on to make
It is extremely important to get this
document right. Mistakes made
later can be very costly.
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Documentation
The systems analyst must document
the clients needs by drafting formal
reports:
 requirements specification
 system specification
6
Design Representations
There are a number of commonly
used forms of design representation
in common use.
Examples include:
 structure diagrams
 pseudocode
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Structure Diagram
A commonly used syntax for
structure diagrams is as follows:
A procedure
A decision
A loop
A single
task
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An example:
A structure diagram allows the design of a
program to be drawn out in diagrammatic
form. Here is an example:
Tax payment
IF earns >
30000
Get details
NO
Low rate
payable
Display amount
to be paid
YES
High rate
payable
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Pseudocode
Pseudocode is another example of a
method of describing a program.
Simple English words are used to
describe the steps of the algorithm
and any refinements made.
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Pseudocode - Example
1.
2.
3.
4.
Display information
Get details
Do calculation
Display answer
Refine
2.1
2.2
2.3
Notice the
numbering
system
2.4
2.5
2.6
step 2
display prompt
get value
while value out of
range
display error
message
get value
loop
Top
level
design
Simple English
words in a familiar
program form
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Hierarchy of Software

A diagram of the hierarchy of
software will


show the relationship between all the
modules of the software
identify modules which contain a call
to other sub modules.
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An Iterative process
It is important to realise that the
software development process is
iterative in nature. This means that
the problem will be revisited a
number of times getting closer and
closer to the required solution on
each time round.
13
CASE Tools
CASE stands for “Computer Aided
Software Engineering”.
A CASE TOOL KIT is a set of integrated
CASE tools that have been designed to
work together and to automate (or
provide automated assistance for) the
entire software life cycle, including
analysis, design, coding and testing.
Using such a toolkit speeds up the
development process in a number of
important ways.
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Fact Finding
Analysis is a fact-finding process, and
there are five key questions that need to
be asked, often repeatedly.
These key questions are:
 WHO?
 WHAT?
 WHERE?
 WHEN?
 WHY?
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Designing the Solution
Once the needs of the user are clearly
understood and documented, software
development can move onto the next stage,
involving the DESIGN of the system.
Design of the User Interface
Design of the structure of the software
Design of the detailed logic of the software
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Implementation
The next stage
involves turning the
carefully structured
design into a
working solution.
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Choosing an Environment
Before we can implement a solution
we must decide on the programming
environment which is most suitable.
Languages are generally designed for
a specific purpose.
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Programming Languages
Language
Algol
Cobol
Comal
BASIC
Fortran
Java
Pascal
Prolog
Purpose
Science
Business
Education
Education
Science and Maths
multimedia
Education
Artificial Intelligence
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Things to Remember...



The code should be modular, - procedures and
functions should be used. Library modules
should be ‘closed’ so that the variables used in
them cannot disturb the code of the rest of the
program.
Meaningful variable names should be used.
There should be internal commentary,
explaining what each section of the code does.
Where a complex algorithm has been
implemented, it is helpful to comment on
several lines of the code, in addition to a general
description of what the module does.
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Things to Remember (2)


Where parameters are being used in a module,
they should be described in the commentary of
the module. This is particularly important in
library modules.
Parameter lists should be small and
manageable. If a procedure or function requires
a set of parameters which is very big, then it is
likely that it is performing more than one
program function. The original design needs to
be revisited, and functionally decomposed.
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Debugging the Solution
A common technique in
trying to debug a piece of
software is to conduct a
structured walkthrough
(step through each line of
logic in the code) using a
structured listing,
which is simply a formatted display or printout of
the code. It is important that the code is written
in such a way that helps the above activities.
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Dry Runs
To complete a dry run the
programmer works through a
section of program code by hand.
This is very useful for locating errors
in both syntax and semantics.
A trace table will normally be used
in this activity.
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Trace Tables
A trace table is
Line no Length Breadth
Area
constructed with a
1
5
column to identify
2
4
3
20
the instruction
4
20
executed and a
column for each
variable.
The programmer works through each line of the
listing changing the appropriate variables.
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Test Data
The expected results from a test data set must be known in
advance, so that they can be checked against the actual
results. You should include test data to demonstrate the
following:
1. “normal” operation of the software, to make sure that
there are no unexpected results in ordinary work.
2. the operation limits of the software, to make sure that
the boundary conditions identified in the design stage
are being handled properly.
3. “exceptions” to the normal operating conditions. This
set will show whether or not the software can react to
unexpected inputs in an effective way, without
crashing.
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Documentation The User Guide


This document should describe how
to use the software.
Ideally there should also be tutorial
files which can take the user
through examples of a piece of
work, and allow them to become
familiar with the commands, and
the various sections of the software.
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Documentation The Technical Guide
This document should provide
information on
 how to install the software
 hardware requirements
 software requirements
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Evaluation

Does the solution meet the user
requirements?

Judge this against a set of criteria








screen layout
help required
user prompts
fitness for purpose
maintainability
robustness
reliability
portability
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Some Definitions

Correctness


A program is correct if it matches the
users requirements
Maintainability

A program will be easily maintained if
it has been written in a way which will
make it easy to change. This will
include



internal commentary
meaningful variable and procedure names
parameter passing
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Some Definitions (2)

Reliability


A program is reliable if it is free from bugs, ie
it must meet the requirements repeatedly
under severe testing
Readability

A program is readable if it is easily
understandable by people other than the
original programmer, ie good internal
documentation, use of white space, etc.
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Some Definitions (3)

Portability


A program is said to be portable if it can be
transferred from one system to another with
minimal adaptation
Efficiency

A program is efficient if it uses the most
appropriate structures for the job. It should
run as fast as possible and not use up more
system resources than are necessary.
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Some Definitions (4)

Robustness


A program is said to be robust if it
does not crash when invalid data is
input or unexpected results are
generated.
Fitness for Purpose

Does the program meet the
requirements?
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Maintenance

Activities identified as part of
maintenance:



corrective (17%)
adaptive (18%)
Perfective (65%)
70
65
60
50
40
30
20
17
18
10
0
%
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Maintenance Costs

Maintenance is very costly. It is
vital that errors are detected at as
early a stage as possible.
100
90
80
70
60
50
40
30
20
10
0
1970s
1980s
2030 ?
% of total development cost
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Factors Affecting
Maintainability






The application being supported
staff mobility
too many versions
not enough documentation
dependence on external
environment
hardware and software stability
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