marr collegehigher software developmentslide 1 the software development process – 4 hours

Marr College Higher Software Development Slide 1

The Software Development Process – 4 hours


Soft

ware

Develo

pm

en

t P

rocess

The Software Development Process

The SDP consists of seven main stages that are followed to develop software.

They are:

1. Analysis

2. Design

3. Implementation

4. Testing

5. Documentation

6. Evaluation

7. Maintenance


Soft

ware

Develo

pm

en

t P

rocess

The iterative nature of the SDP

The SDP is iterative as any of the stages may be revisited throughout the project.

Example:

If an error is found in the maintenance stage (after release) then the implementation stage will be revisited to fix the code.


Soft

ware

Develo

pm

en

t P

rocess

The Software Specification

The Software Specification is a document that defines the scope and boundaries of the project and becomes legally binding between the client and the developers.


Soft

ware

Develo

pm

en

t P

rocess

Personnel involved the SDP

Client - commissions the software project as a result of an identified ‘need’.

Systems Analyst – Investigates the client’s current system and designs the new or upgraded system.

Project Manager – Project leader who manages the project and the development team. Ensures deadlines being met and resources are in place.

Programmer – Implements the designs (pseudocode etc.) into program code.

Independent Test Group – tests the software to identify any errors by testing subroutines, modules and the completed program.


Soft

ware

Develo

pm

en

t P

rocess

Analysis

The Systems Analyst meets with the client, interviews and observes users of the current system and identifies what the program has to do, in a process known as Requirements Elicitation.

The result is the production of the Software Specification.


Soft

ware

Develo

pm

en

t P

rocess

Design

The design process is methodical and involves designing and representing algorithms as pseudocode and/or structure diagrams.


Soft

ware

Develo

pm

en

t P

rocess

Design

Algorithm

An algorithm is a sequence of actions that, when performed in the correct order, will solve a problem or task in a finite number of steps.

Example:

Here is a simple algorithm to convert a Fahrenheit temperature to Celsius:

1 Subtract 32 from Fahrenheit temperature2 Multiply by 5/9ths to get Celsius temperature

So,

98.6°F - 32 = 66.666.6 * 5/9ths = 37°C

What happens if you swap steps 1 and 2 - do you get the same answer?


Soft

ware

Develo

pm

en

t P

rocess

Design

Pseudocode

Pseudocode is a design notation that combines English language and Maths with programming language constructs.


Soft

ware

Develo

pm

en

t P

rocess

Design

Pseudocode

Note:

Pseudocode is not specific to any programming language. It is a design notation that can be implemented by programmers in any programming language

Here is the Fahrenheit conversion algorithm represented as pseudocode to be implemented as program code:

1.1 Get temp(°F)

1.2 Set temp(°F) = temp(°F)-32

1.3 Set temp(°C) = temp(°F)*0.556

1.4 Display temp(°C)

1.1 Get temp(°F)


1.3 Set temp(°C) = temp(°F)*0.556



Soft

ware

Develo

pm

en

t P

rocess

Design

Structure Diagram

A Structure Diagram is another design notation that represents algorithms in a chart or graphical form

Here is the Fahrenheit conversion algorithm represented as a structure diagram to be implemented as program code:

Covert °F to °C

1.1 Get temp(°F)

1.3 Set temp(°C) = temp(°F)*0.556




Soft

ware

Develo

pm

en

t P

rocess

Design

Flow chart

A flow chart is another design notation that shows the sequence of operations required to complete a task.

This chart shows the sequence of reading customer accounts and calculating the amount due for each customer.

After an account has been processed, the program loops back to process the next one.


Soft

ware

Develo

pm

en

t P

rocess

Design

Top-down design is where a task or problem is broken down into stages that can be solved as individual parts.

This structure diagram illustrates a top-down approach to identifying the stages of the problem solution.

Top-down design

Is the process of breaking a problem down in to sub-problems.


Soft

ware

Develo

pm

en

t P

rocess

Design

Stepwise Refinement

Stepwise-refinement is the process of refining stages down into steps. Each step can then be coded in a programming language.


Soft

ware

Develo

pm

en

t P

rocess

Implementation

This is where the programmer(s), overseen by the project manager, convert the pseudocode (algorithms) into programming code e.g. Visual Basic, C++, Java etc.

‘Program Code

tempF = txtTempF.Text

tempF = tempF-32

tempC = tempF*0.556

lblTempC = temp(°C)

‘Program Code

tempF = txtTempF.Text

tempF = tempF-32

tempC = tempF*0.556

lblTempC = temp(°C)

Pseudocode

1.1 Get temp(°F)


1.3 Set temp(°C) = temp(°F)*0.556


Pseudocode

1.1 Get temp(°F)


1.3 Set temp(°C) = temp(°F)*0.556


A formatted printout of the program code is known as a structured listing. It includes indentation, white space and internal commentary.


Soft

ware

Develo

pm

en

t P

rocess

Testing

Testing should be both systematic and comprehensive i.e. methodical with test reports of predicted and actual results kept, and tested under all operational situations with a full range of test data.

The three types of testing are normal, extreme and exceptional.

Example

Program should only accept whole values in the range 0 to 100:

Normal data: 2, 34, 66 etc.

Extreme data: 0,100

Exceptional: -1, 156, abc, 2.9 etc.

Example

Program should only accept whole values in the range 0 to 100:

Normal data: 2, 34, 66 etc.

Extreme data: 0,100

Exceptional: -1, 156, abc, 2.9 etc.

Acceptance (beta) testing is when independent test groups and/or the client try out the software and report back any bugs to the development team prior to final release.


Soft

ware

Develo

pm

en

t P

rocess

Documentation

To produce documentation to be distributed with the software. The two main documents are the user guide and the technical guide.

1 User Guide

A set of instructions on how to install and use the software perhaps including tutorials and FAQS. Can be in both a booklet or electronic format.

2 Technical Guide

Describes hardware requirements e.g. CPU, RAM space on hard disk etc.


Soft

ware

Develo

pm

en

t P

rocess

Evaluation

An evaluation report is prepared and supplied to the client with the release of the software.

Evaluation

Reliable

No design faults

Correct output

Portable

Cross platform

Efficient

Low processor and memory overheads

Maintainable

Readable i.e. internal commentary, indentation etc.

Modular i.e. uses procedures and functions.

Robust

Copes with errors

Does not crash

Fit for purpose

Does the program meet the spec?


Soft

ware

Develo

pm

en

t P

rocess

Maintenance

Begins once the software has been released and put into use. Involves the client who uses the software and the programmers to make any necessary changes.

There are 3 types of maintenance.

Corrective: Fixing any errors that were not detected during the testing phase.

Adaptive: To alter the software to work with a new operating system or new hardware.

Perfective: Add new functionality at the request of the client.

Corrective: Fixing any errors that were not detected during the testing phase.

Adaptive: To alter the software to work with a new operating system or new hardware.

Perfective: Add new functionality at the request of the client.

Corrective maintenance is part of the contract whereas adaptive and perfective are usually at additional expense to the client.


Languages and Environments – 6 hours


Lan

gu

ag

es a

nd

En

vir

on

men

tsProcedural Languages

Programs follow a sequence from start to finish and can be split into sub-programs called procedures.

Languages such as Pascal, Comal and Basic are procedural and nowadays are mainly used for learning programming.

Sample Pascal code


Declarative Languages

Declarative (logic) programming has no fixed start or end point; are collections of facts and rules; and use pattern matching to answer queries.

Lan

gu

ag

es a

nd

En

vir

on

men

ts

Declarative languages such as Prolog and LISP are used predominantly in the field of Artificial Intelligence.

Here are some facts:

Parent (Liz, Tom). means that Liz is a parent of TomFemale (Liz). means that Liz is femaleMale(Tom).Parent(Bert, Tom).

Here is a rule:

Mother(X, Y) :- means that X is a mother of Y IF Parent(X, Y), Female(X) X is a parent of Y AND X is female!

Query could be Mother(X, Tom) which would give the answer X=Liz


Event-driven Languages

An object-oriented programming paradigm where objects on the interface have their own code attached e.g. a command button.

Visual Basic and Java are examples of event-driven languages.

The code is executed in response to events e.g. form load, button click etc.

Lan

gu

ag

es a

nd

En

vir

on

men

ts


Lan

gu

ag

es a

nd

En

vir

on

men

ts

Programs written in high-level languages need to be translated into low-level (machine code) for processing and executing by the CPU. This is done by a translator program.

Translators

There are two types of translator program:

• interpreters

• compilers


Lan

gu

ag

es a

nd

En

vir

on

men

ts

Interpreter programs translate HLL code into machine code one line at a time.

Advantages:

easy to find errors

good for learners

Disadvantages:

programs slow as have to be continually interpreted

interpreter program always in memory

Interpreters


Lan

gu

ag

es a

nd

En

vir

on

men

ts

A Compiler program translates the whole program (source code) into a machine code version (object code) that can be run without the compiler being present.

Advantages:

programs execute fast as CPU ready

translator program only needed at the time of compiling

different compilers can be written for different platforms.

Compilers

Disadvantages:

slow to compile as whole program translated

also may not run if syntax errors.


Scripting Languages

Programs written as scripts are used to automate or extend the functionality of software applications.

Lan

gu

ag

es a

nd

En

vir

on

men

ts

A Macro is a script written in Visual Basic for Applications (VBA).

The user records a series of actions in an application such as MS-Excel.

Code is generated and saved as a program script.

The macro can then be assigned to a keystroke.

Used to simplify and repeat complex or frequently used commands.


Module Libraries

A Module Library is a pre-written and pre-tested collection of subroutines and functions which the programmer can use to aid the development of the final program.

Lan

gu

ag

es a

nd

En

vir

on

men

ts

Advantages include:

No code has to be written for problems already solved

The code will have been checked for any errors

The modules will be well documented


HLL Programming Constructs – 14 hours


String Operations

The two string operations are concatenation and substrings.

HLL P

rog

ram

min

g C

on

str

ucts

Concatenation is the joining together of two strings.

This example will output “Good morning!” to a text box.

Substrings are parts of strings that are extracted and used in some way.

‘Example

first = “Good “

second = “morning!”

whole = first & second

lblMsg.Caption = whole

‘Example

first = mid$(“Phil”,1,1)

second = mid$(“Mitchell”,1,1)

initials = first & second

lblMsg.Caption = initials

This example will output “PM” to a label.


Formatting of Input / Output

Data can be input via text boxes, input boxes etc.

Data can be output to the screen by setting properties such as font, colour etc.

Concatenation can be used to output strings and numerical data.

HLL P

rog

ram

min

g C

on

str

ucts

‘Example

lblMsg.Caption = “The total is “ & total & “!!”

‘Example

txtAve.Text = Format(average,”.00”)

‘Example

txtAve.Text = Format(average,”.00”)

Use of pre-defined functions may also format output.


Multi-way Selection

The CASE statement improves the IF..THEN..ELSE construct where more than two conditions are possible.

HLL P

rog

ram

min

g C

on

str

ucts ‘Implement using CASE

Select Case mark

Case Is >= 70

grade = “A"

Case Is >= 60

grade = “B"

Case Is >= 50

grade = “C"

Case Else

grade = “Fail"

End Select

‘Algorithm using nested IFs

If mark >= 70 Then

grade = “A"

Else

If mark >= 60 Then

grade = “B“

Else

If mark >= 50 Then

grade = “C"

Else

grade = “Fail"

End If

End If

End IfCASE makes the code more readable so aids maintenance.


Variables

A variable is the name used to store a single item of data within a program.

HLL P

rog

ram

min

g C

on

str

ucts

Examples

Integer variables store whole numbers e.g. Dim age As Integer

Real variables store decimal numbers e.g. Dim price As Single

String variables store text e.g. Dim pname as String

Boolean variables store either TRUE or FALSE e.g. Dim Swaps As Boolean


1D ArraysH

LL P

rog

ram

min

g C

on

str

ucts

An array is a name given to a list of items of data in a program. The list is stored in contiguous memory locations.

Here is an array nums(10) of integers between 1 and 9:

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

3 6 2 5 6 3 9 4 5 7

Here is some VB code to setup and array:

‘Example: 1D array

Dim nums(10) As Integer

Here is some VB code to setup and array:

‘Example: 1D array

Dim nums(10) As Integer

Here is some VB code that would input data to an array:

‘Example: Input to array

For c = 1 To 10

nums(c) = inputbox(“Enter number etc.

List1.additem nums(c)

Next c

Here is some VB code that would input data to an array:

‘Example: Input to array

For c = 1 To 10

nums(c) = inputbox(“Enter number etc.

List1.additem nums(c)

Next c


Modularity

Well written code makes use of modular programming. This simply means that programs are organised into modules or sub-programs.

HLL P

rog

ram

min

g C

on

str

ucts

Advantages

Each sub-program can be developed and tested as a standalone program

Bugs can be located within a specific sub-program

Maintenance can be carried out on each

Programs can be sub-divided and developed by many programmers

The two main types of modules are subroutines (procedures) and functions.


ProceduresH

LL P

rog

ram

min

g C

on

str

ucts

A procedure is a subroutine that performs a specific task in a program.

A procedure can be invoked by:

a) an event e.g. Private Sub cmdCalculate_Click()

b) being called when needed e.g. Call Validate

Here’s how to create a procedure in VB6:

Private Sub InputNames()

Statements

End Sub


Functions

A function is a subroutine that always returns a value e.g. a function could be used to return the result of a calculation.

HLL P

rog

ram

min

g C

on

str

ucts

Note: The value returned from the function must always be assigned to a variable or a control!

Note: The value returned from the function must always be assigned to a variable or a control!

If CalcTax()was a function then you could return a value to a label

e.g. lblAmount.Caption = CalcTax()

Here’s how to create a function in VB6:

Private Function CalcTax () As Single

Statements

End Function

or you could return a value to an expression

e.g. Amount = Estimate * .2 + CalcTax() * .14


User-defined Functions

A user-defined function is a subroutine that is coded by the user and ‘called’ by another section of program code. It does not depend on an event.

HLL P

rog

ram

min

g C

on

str

ucts


Global Variables

Global variables are declared at the start of a program and can be used anywhere in the program.

HLL P

rog

ram

min

g C

on

str

ucts

Pros and cons

Can be used anywhere in the program

Declared once at the start

If value changes then changes for the rest of the program

Can be changed by mistake


Local VariablesH

LL P

rog

ram

min

g C

on

str

ucts

Local variables are declared within a procedure or function and can only be used by that subroutine.

Pros

Different variables can have the same name

Save memory as created and destroyed during subroutine runtime

Make subroutines ‘standalone’ so easy to reuse in other programs

Reduce risk of accidental change of global value


Parameter PassingH

LL P

rog

ram

min

g C

on

str

ucts

The two methods of parameter passing are:

i. By reference (in and out)

A parameter is simply the value of a variable that can be passed between subroutines.

age = 25

variable parameter

SubroutineIN

SubroutineIN OUT

ii. By value (in)


By reference H

LL P

rog

ram

min

g C

on

str

ucts

Parameter passed is the actual variable itself. Any changes to the parameter persist beyond the call i.e. change the original value.

Subroutine A

25age

age = 25

Subroutine B

Private Sub check (ByRef age)

25age

age = 42

42age

42age

Note: An array should always be passed by reference due to memory overheads.


By valueH

LL P

rog

ram

min

g C

on

str

ucts

A copy of the current value of parameter is passed in and any changes do not affect the original value.

25age

Subroutine A Subroutine B

25a

age = 25 Private Sub check (ByVal a)

42a

a = 42

Note: In sub B the variable a is an alias i.e. a copy of the actual parameter.

alias


Advantages of parameter passingH

LL P

rog

ram

min

g C

on

str

ucts

There are a number of advantages:

Greater control of data flow

Reduced risk of accidental change

More efficient use of memory

Sub-programs are more ‘self-contained’

Improved reliability and robustness

Here’s how to pass parameters in VB6:

Call AddVat (cost, total)

Private Sub AddVat (ByVal c, ByRef total)

statements

End Sub


Standard Algorithms – 12 hours


VB6 Code

Pseudocode

1 Input Validation

Validates program input and rejects invalid data.

Sta

nd

ard

Alg

ori

thm

s

1.1 Get and store value

1.2 Loop WHILE data is out with range

1.3 Display error message

1.4 Prompt user to re-enter value

1.5 End loop

num = InputBox (“Enter number between 1 and 10”)

Do While num < 1 Or num > 10

MsgBox “Must be num between 1 and 10”

Num = InputBox (“Enter number between 1 and 10”)

Loop


2 Linear Search

Searches a list for a target value.

Sta

nd

ard

Alg

ori

thm

s

Pseudocode

VB6 Code

2.1 Get and store target value

2.2 Loop for each item in the list

2.3 If current item = target value THEN

2.4 Display item and its location in list

2.5 End if

2.6 End loop

target = InputBox (“Enter target value”)

For p = 1 To 10

If array(p) = target Then

picResult.Print target & “found at position “ & p

End If

Next p


3 Counting Occurrences

Counts the number of times (frequency)

Sta

nd

ard

Alg

ori

thm

s

Pseudocode

3.1 Set counter = 0

3.2 Get and store target value

3.3 Loop for each item in the list

3.4 If current item = target value THEN

3.5 Increment counter

3.6 End if

3.7 End loop

VB6 Code

times = 0

target = InputBox (“Enter target value”)

For p = 1 To 10

If array(p) = target Then

times = times + 1

End If

Next p

Remember to output e.g. to a label or control array etc.

Remember to output e.g. to a label or control array etc.


Pseudocode

4 Finding Maximum

Find largest value in a list.

Sta

nd

ard

Alg

ori

thm

s

4.1 Set max = first item

4.2 Loop for each remaining item in the list

4.3 If current item > max then

4.4 Set max = current item

4.5 Set position = counter

4.6 End if

4.7 End loop

VB6 Code

max = array(1)

For p = 2 To 10

If array(p) > max Then

max = array(p)

pos = p

End If

Next p


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Finds the smallest value in a list….


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Set min to first item in list…

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Is 3 less than 21?

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

If yes then set min as 3.

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Is 56 less than 3?

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

If no then do nothing.

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Is 2 less than 3?

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

If yes then set 2 equal to min.

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Is -9 less than 2?

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

If yes then set min equal to -9.

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Is 5 less than -9?

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s


21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

Is 3 less than -9?

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s


21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


5 Finding MinimumS

tan

dard

Alg

ori

thm

s

-9 is the smallest value in the list.

21 3 56 2 -9 5 3

(1) (2) (3) (4) (5) (6) (7)

min


Pseudocode

5 Finding Minimum

Find smallest value in a list.

Sta

nd

ard

Alg

ori

thm

s

5.1 Set min = first item

5.2 Loop for each remaining item in the list

5.3 If current item < min then

5.4 Set min = current item

5.5 Set position = counter

5.6 End if

5.7 End loop

VB6 Code

min = array(1)

For p = 2 To 10

If array(p) < min Then

min = array(p)

pos = p

End If

Next p


TASK – Find Min and Max

Write a program that will:

a) allow the user to input 10 scores between 1 and 6. The scores can be real i.e. 2.3, 5.6 etc.

b) Calculate the total score i.e. each of the scores totalled up!

c) Find the minimum and maximum score and subtract from the overall total to obtain a final score. Hint: final = total – (min + max) Use a function!

d) Display all the scores on screen, along with the minimum, the maximum and the final score.

e) Extension: Adapt the program to display each score on screen in ascending (sorted) order as it is entered by the user.

Have fun!!!

McLean

Sta

nd

ard

Alg

ori

thm

s

marr collegehigher software developmentslide 1 the software development process – 4 hours

Documents