Chapter 12 Software development

12.1 Program development lifecycle

Program development lifecycle – the process of developing a program set out in five stages:

• analysis
• design
• coding
• testing
• maintenance

Waterfall model – a linear sequential program development cycle, in which each stage is completed before the next is begun

• pros: easy to manage
• cons: not suitable for long, complex projects; difficult to change the requirements at a later stage

Iterative model – a type of program development cycle in which a simple subset of the requirements is developed, then expanded or enhanced, with the development cycle being repeated until the full system has been developed

• pros: easier to test and debug smaller programs; more flexible as easier to alter requirements
• cons: not suitable for short simple projects

Rapid application development (RAD) – a type of program development cycle in which different parts of the requirements are developed in parallel, using prototyping to provide early user involvement in testing

• pros: reduced overall development time; very flexible as requirements evolve from feedback during development
• cons: system under development needs to be modular; not suitable for short simple projects

12.2 Program design

Structure chart – a modelling tool used to decompose a problem into a set of sub-tasks. It shows the hierarchy or structure of the different modules and how they connect and interact with each other

DECLARE radius : REAL
DECLARE answer : REAL
CONSTANT pi ← 3.142

FUNCTION calculateVolume (radius:real) RETURNS real
  RETURN (4 / 3) * pi * radius * radius * radius
ENDFUNCTION

FUNCTION calculateSurfaceArea (radius:real) RETURNS real
  RETURN 4 * pi * radius * radius
ENDFUNCTION

PROCEDURE inputRadius
  OUTPUT "Please enter the radius of the sphere "
  INPUT radius
  WHILE radius < 0 DO
    OUTPUT "Please enter a positive number "
    INPUT radius
  ENDWHILE
ENDPROCEDURE

PROCEDURE outputAnswer
  OUTPUT answer
ENDPROCEDURE

CALL inputRadius
WHILE radius <> 0
  OUTPUT "Do you want to calculate the Volume (V) or Surface Area (S)"
  INPUT reply
  IF reply = "V"
    THEN
      answer ← calculateVolume(radius)
      OUTPUT "Volume "
    ELSE
      answer ← calculateSurfaceArea(radius)
      OUTPUT "Surface Area "
  ENDIF
  CALL outputAnswer
  CALL inputRadius
ENDWHILE

A finite state machine (FSM) is a mathematical model of a machine that can be in one of a fixed set of possible states. One state is changed to another by an external input, this is called a transition. A diagram showing the behaviour of an FSM is called a state-transition diagram.

12.3 Program testing and maintainence

Trace table – a table showing the process of dry- running a program with columns showing the values of each variable as it changes Run-time error – an error found in a program when it is executed; the program may halt unexpectedly

Program testing

Several types of test data need to be used during testing:

• Normal test data
• Abnormal test data that should be rejected by a program as it is unsuitable or could cause problems
• Extreme test data - data on the limit of that accepted by a program
• Boundary test data - data on the limit of being accepted by a program or just outside the limit of being accepted

Testings as the program is being developed:

• White-box testing - the detailed testing of how each procedure works. This involves testing the structure and logic of every path through a program module
• Black-box testing - tests a module’s inputs and outputs
• Integration testing - the testing of any separately written modules to ensure that they work together, during the testing phase of the program development lifecycle

When the program has been completed:

1. Alpha testing - The completed, or nearly completed, program is tested in-house by the development team
2. Beta testing - The completed program is tested by a small group of users before it is generally released
3. Acceptance testing - used for the completed program to prove to the customer that it works as required in the environment in which it will be used

Program maintenance

• Corrective maintenance - used to correct any errors that appear during use
• Perfective maintenance - used to improve the performance of a program during its use
• Adaptive maintenance - used to alter a program so it can perform any new tasks required by the customer