Week 2

Question 1

Meaning by Generalisation

Answer 1

• You are given a specific problem
• You decompose the problem into parameters, such that it can solve other type of problems

Question 2

Methods of Generalisation

Answer 2

• Generalised by paramets and not via global variables

Question 3

IEEE classification

Answer 3

• Mistake: human action, causing a fault
• Defect, fault: anomaly in a product that can somehow lead to a failure
• Failure: product deviates from requirements during use, Or
• Error: difference between actual and expected result

Question 4

Economy of Defects

Answer 4

The longer a defect is undiscovered: the higher the cose to remove it
- The cost grows exponentially in distance between the injection and elimination

Question 5

Why does defects decrease the predictability of a project

Answer 5

• Hard to know how long to remove a defect
• Cost (time) of defect localisation and repair are extremely variable

Question 6

Kinds of Engineering Mistakes

Answer 6

• Misunderstanding a customer
• Misinterpreting a written requirement
• Overlooking a case in analysing the requirements
• Adopting an incorrect algorithm
• Making an unwarranted assumption when implementing a method
• Making a type error when entering the code

Question 7

How to deal with mistakes

Answer 7

1. Admit that people make mistakes
2. Prevent them as much as possible
3. Minimise consequence: fault tolerance, defensive programming
4. Detect the presence of defects as early as possible
5. Localise defects
6. Repair defects
7. Trace them: root causes and passible other consequence
8. Learn from them

Question 8

Techniques for Construction test Cases

Answer 8

• Boundary analysis: pick values on and near boundaries
• Equivalence classes: pick a case from every equivalence class
• Statement, branch, and path coverage
• Random input

Question 9

What is Boundary analysis

Answer 9

pick values on and near boundaries

Question 10

What is Equivalence classes

Answer 10

pick a case from every equivalence class

Question 11

How to decide on pass vs. fail when making a test case

Answer 11

• Select trivial or highly structured input with known output
• ‘Manually’ determine expected output
• Check correctness of output via ‘inverse’ process;
• Use alternate implementation to compute expected output; e.g. using a slower but simpler algorithm
• Cross check the consistency of implementation; e.g. check whether sorting a list and sorting a permutation of that same list yield the same output

Question 12

What is a Robust Program

Answer 12

continues to behave reasonably in the presence of a defect, a violated precondition call

Question 13

What is the best way a robust program deals with default

Answer 13

At best: provide an approximation of defect-free behavior. Also known as graceful degradation.

Question 14

What is the worst way a robust program deals with default

Answer 14

At worst: halt with a meaningful error message without causing damage.

Question 15

What is a partial Function

Answer 15

Do nothing when given a wrong call: “Its up to the client to call it correctly”

Question 16

What is a return special value for a robust program

Answer 16

The program returns a special value, which we know is not a legal value, to show that the function was not called properly.

Question 17

Why can’t we use special values for a robust program?

Answer 17

Because there may not be a specific value that is not a legal a value

Question 18

What are the three ways to deal with violated precodition (make a robust program1)

Answer 18

• Do Nothin
• Return a special value
• Use an exception

Question 19

What is the best way to deal with a violated precondition (make a robust program)

Answer 19

• Use an exception

Question 20

Advantages of robustness

Answer 20

• Easier to locate an error

Question 21

Disadvantages of robustness

Answer 21

• More code
• Runtime overhead in checking the precondition, even if satisfied
• Runtime overhead in throwing, propagating, catching exceptions.