Higher Grade Computing Studies
1. Software Development Cycle
Introduction
• The development of a piece of software from scratch is a process
that takes considerable time. We can classify these stages thus :
1.
2.
3.
4.
5.
6.
7.
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Analysing the problem:
Designing the program:
Implementing the design:
Testing the design:
Documenting the design:
Evaluating the design:
Maintaining the software:
Can we do it?
How do we do it?
Writing the program
Making sure it works
User guides, Technical manuals
Limitations and improvements
Correcting, adapting and
perfecting
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Iterative
• The cycle is iterative. Iteration means to follow through a
process more than once before concluding it. An iterative
process is one that incorporates feedback and involves an
element of repetition.
• The implementation stage can be iterative because testing
may show that the program doesn’t run properly, so the
programmer will have to revisit the design and
implementation stages.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Personnel
• The clients are the persons who require the new system.
They are the ones who need the new software developed.
• The project manager is the leader of the software house.
This person takes sole responsible for the whole project and
must supervise all steps and stages required. S/he will liaise
with the systems analyst and keep the whole project on track.
S/he will also ensure that programmers meet deadlines and
have the resources they need, will deliver any reports on time
and be kept fully aware of test results.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Personnel
• The Systems Analyst works for a software house and
agrees with the client the exact nature and specification of the
software to be written.
• The programmer is responsible, either individually or as
part of a team, for turning the design into programming code.
• The Independent Test Group (ITG) carries out the testing
of the software. They will test each individual part of the
program, larger sections of the program and finally the
finished product.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Analysis
Key Task: To define the extent of the software task to be
carried out.
Personnel: Client and Systems Analyst
Documentation: The legally binding Software Specification
Report
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Analysis
• Analysis is the most important part of the process. Changes
can be identified early on thus reducing the amount of extra
work and cost involved in trying to make changes later.
• Analysis is a fact finding
process aimed at answering the
following questions :
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• WHO?
• WHAT?
• WHERE?
• WHEN?
• WHY?
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Analysis
• Analysis starts with discussions between the client and a
systems analyst. The analyst will carry out three main
tasks.
• observe the system currently in use.
• clarify the system currently in use.
• model the system currently in use.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Analysis
• The particular skills that an analyst needs to have would be:
• to be able to extract the needs of the client who may not be
technically skilled.
• to be able to document these needs in some formal way.
• to be able to communicate these needs to the people who
will actually design the computerised system.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Analysis - Extracting Needs
• This can be called requirements elicitation and can take some
time. Difficulties may arise due to either the client’s lack of
awareness of the capabilities of the computerised system or the
analyst’s lack of knowledge of the client’s business operations.
• The analyst will proceed through:
• a series of interviews with the client’s management team,
• make observation notes of what actually happens in the
workplace,
• use questionnaires and literature, e.g. manuals, to
determine how the existing system operates.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Analysis - Documentation
• These discussions will lead to a legally binding requirements
specification. This is a detailed document which indicates what the
client wants the design team to do and will include a system
specification.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Design
Key Task: To design a method of solving the stated problem.
Personnel: Systems Analyst and Project manager
Documentation: A description of how the problem will be
solved. This algorithm may be text based (pseudocode) or
graphical (structured diagram)
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Design
• Design involves planning the solution to the problem. This would
not take place until the specification document had been agreed
between the client and the programmer. As with analysis, it is
crucial to detect errors at this stage rather than later.
• Design can be broken down into :
1. Design of the structure
2. Design of the detailed logic
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Design Methodology - Modular
• A large computer program can be organised into smaller parts
called modules, which can be developed at the same time by
different programmers and programming teams.
• Modules can be designed, programmed and maintained
independently of one another.
• Ideally each module should:
• be small
• be self contained so it can be
• do one task only
saved and used in other programs.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Design Methodology - Modular
• There are several design techniques. The one we use is called Top
Down Design. In this method, the problem is broken down into
smaller sub problems that are then divided in turn into even smaller
ones.
• This continues until the sub problems are manageable enough to be
coded - step wise refinement.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Design Notations
• The design stage results in a detailed algorithm - a sequence of
operations needed to solve the problem. There are several design
notations, or methods of representing an algorithm, including:
• pseudocode
text is in English but easily converted into
language code. Its advantage is it will be
close to the final coded program.
• structure chart
a diagram showing the component sub
problems and how they are linked. It can
show the structure of the whole program
in a small space.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Design - Pseudocode
1.
2.
3.
4.
Notice the
numbering
system
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Display information
Get details
Do calculation
Display answer
Top level
design
Refine step 2
2.1 display prompt
2.2 get value
2.3 while value out of range
2.4
display error message
2.5
get value
2.6 loop
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Design - Structure Chart
In/out
In
Data Flow
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Implementation
Key Task: To write code in a chosen programming
language.
Personnel: Programmer and Project manager
Documentation: A structured listing of the programming
code showing formatting features such as commands in
bold, indentation, etc.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Implementation - Language Choice
• For most problems, however, a suitable high level language may
be required. Some high level languages have special applications
and are suited to certain problem types - for example, Prolog for
Artificial Intelligence.
• Others are more general and can be used to solve a wide range
of problems - for example, Comal can be used to solve a wide
range of programming tasks.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Structured Listing
• A structured listing is a program printed on paper that uses
indentation (formatting) to show the structure of the program.
• A structured listing can also highlight keywords and variable
names in a different text colour.
• Advantages
• Easy to understand the structure of the whole program.
• Mistakes are easier to spot.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Structured Listing
• A structured listing should be readable.
Readable : Easily understood by others e.g. use of meaningful
variables, constants, procedure and function names, Suitable
internal comments. Good layout with spaces between sections.
Description of parameters. Parameter lists are kept short.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Testing
Key Task: To test that the program meets the specification.
Personnel: Independent Test Group (ITG)
Documentation: Set of test data and test reports. The test
data will have predicted (before running) and actual (after
running) output.
22
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Testing
• Many organisations now employ Independent Test Groups
who return the program to the programmers for correction
after testing.
• The program is now tested using many sets of test data to
check that it gives the correct output under all possible
conditions. It is important that the expected results from the test
should be known before the test is carried out so that the actual
results can be checked.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Testing - Test Data
• Testing is usually done with three types of test data:
1. Normal data - typical data that would be expected.
2. Extreme data - the data is at the extreme limits allowed. e.g.
if an age is to be between 0 and 120 then these two values are
tested.
3. Exceptional data - the data is not suitable for the program e.g.
(i)
values outside agreed ranges
(ii)
letters instead of numbers.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Testing - Stages of Testing
• Testing is itself a structured process starting with individual
lines of code and building up to a test of the entire system.
1. Structured Walkthrough - Each line of logic in the code is
stepped through using a printed listing.
2. Component or procedural testing - A procedure can be
tested by creating another procedure called a driver procedure
to provide the necessary data. Once the test has proved
satisfactory, the driver procedure is deleted.
25
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Testing - Stages of Testing
3. Module testing - This involves testing a number of already
tested individual procedures to make sure that they link together
correctly as a module. Again a driver procedure is used to call the
module procedures in the correct sequence.
4. Sub System testing - In the same way, groups of modules
which are designed to communicate are tested.
5. System testing - Finally, the overall system made up of
tested sub systems is tested.
26
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Testing - Stages of Testing
6. Beta testing - The system may now be trialled with a number of
selected users in the real world. A so called ‘beta version’ is issued
to users who test it under working conditions and report any faults
to the design team. These results are often used to make final
changes just before publication.
27
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Testing - Error Detection & Removal
• There are basically two types of errors:
1. Syntax errors - errors in the code e.g. missing ; where the
rules of the language are broken.
2. Run time errors - errors that only occur when the program is
executed such as incorrect variable names or division by zero.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Documentation
Key Task: To produce documentation to be distributed with
the software.
Personnel: Client, Systems Analyst and programmer
Documentation: User Guide and Technical Guide
29
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Documentation
• All software comes with two essential pieces of documentation.
1. The Technical Guide
• How to install the software, its memory and processor
requirements, version number, help files of systems extensions
needed.
• Reference section on trouble-shooting system problems.
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Documentation
2. The User Guide
• A beginners (‘getting started’) guide often in the form of a
tutorial in which the USER goes through a number of worked
examples.
• A User manual explaining how to use the package.
Frequently, these may be provided in electronic form with an
interactive help and tutorial system. The user will have the
option to print these if needed.
31
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Evaluation
Key Task: To report upon the quality of the software
according to given criteria.
Personnel: Systems Analyst and Project manager
Documentation: A Project report accompanying the
software to the client. It compares the software to the
original specification and comments on the quality of the
software.
32
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Evaluation
• The finished working program is now compared with the
original specification. This involves judging the software against a
set of criteria such as :
• a list of the original user requirements
• the quality of the HCI
• choice of suitable language
• attributes of good programming style
• quality of testing
• choice of language
Higher Computing
33
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Maintenance
Key Task: To make changes to the software after it has been
handed over to the client.
Personnel: Varies but programmer and client will certainly
be involved
Documentation: A Maintenance report will detail and
confirm the maintenance carried out.
34
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Maintenance
• A company will have three maintenance activities;
1. Corrective
• Emergence of undetected errors.
• Need to be reported and corrected
2. Adaptive
• Code overtaken by developments in operating
systems, CPUs, peripherals leading to code failure or
less effective operation.
• System needs to be adapted to new conditions
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Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Maintenance
3. Perfective (65% of the time)
• Users request changes such as adding new or
altering existing functions or general improvements.
36
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Desirable Characteristics Of Software
1. Robust : Input should appear as typed (echoed). Input should
be validated and the user asked for re-entry. Should not crash on
invalid input. All possible errors trapped e.g. division by 0.
2. Reliable : Free from error. Works for all allowed inputs.
3. Portable : Can be easily adapted for use on other machines by
avoiding the use of machine specific commands.
4. Efficient : make good use of time and memory.
37
Higher Computing
Software Development
S. McCrossan
Higher Grade Computing Studies
1. Software Development Cycle
Desirable Characteristics Of Software
5. Maintainable : Easy to change, upgrade and adapt. Needs to
be modular i.e. use of procedures, functions and local variables
are important, along with short main programs. Use should be
made of pre-written Library modules to avoid unnecessary
writing of code.
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Higher Computing
Software Development
S. McCrossan