Revise - 2.3 - Robust programs

• Computing
• Upper Secondary (Key Stage 4)
• GCSE

Everything you know about defensive design. (Methods)

Defensive design 

Aspire: To identify key methods of defensive design.

Conquer :Solve exam level questions. 

Why? 

We need to consider how end users will make use of the product.

We need to anticipate any way they may misuse the software, either willingly on unwillingly. 

Methods

• Anticipate Misuse
• Maintain code
• Verification
• Validation
• Reduce errors through testing

Anticipate misuse. 

Planning ahead and taking steps to prevent potential misuse.

This takes place during the design and testing process before product release. 

Input validation

This is the process of checking data entered by the end user to ensure it meets specific criteria. 

Example: Dates, phone numbers. 

Data Validation methods. 

Range check

Format check

Presence check

Length check

Type check

The input must fall within a specified range

The data must be in the correct order.

 The data must be of a specified data type

Checks if data has been entered.   

The input must not be too long or too short.

Length Check

Has a minimum amount of characters

Range Check

Falls between two set values

Presence Check

Must be filled in - cannot be blank

Format(type) check

Must be in correct format or datatype

What is authentication?
How is it different to Validation?

Authentication

Authentication is the process of a user confirming that they are who they say they are on a computer system.

Methods: 

• Passwords
• 2FA
• Biometrics, cards, Pin, Secret question.

Maintainability

The purpose of maintainability is to ensure that, over time, a program can be easily maintained.

This could mean fixing errors, making changes or additions. 

Describe TWO ways to more easily maintain your coded solutions [4]

Easy to Maintain

• Add comments - to explain key features and understanding to code
• Indentation - to separate different statements.  Makes code easier to read
• Sensible naming - of variables/procedures to they are recognisable easily
• Use functions/procedures - to break up reusable code to avoid duplications

Describe the purpose of testing code [2]

Identify the two types of error you will encounter when programming [2]

LOGICAL

SYNTAX

a = 5

b = 2

C = a+b

print(c)

primt("hello world")

if a>b

  print("bigger")

else

 print("smaller")

name = "Bob"

print("name")

if a>18:

  print("adult")

else:

 print("child")

while a !=0:

  print(a)

Test types

• Valid - Test that falls in the expected range of a request. 
• Invalid  - Data of the correct data type, but does not meet the rules. 
• Erroneous  - Entering the wrong data type.
• Boundry - Data at the min and max of a range.

A system is made to store student test scores that are out of 0 to 100.
Identify suitable test data to run a valid, invalid, boundary and erroneous tests. Separate your answers with commas [4]