1.4) Quality Costs

Question 1

Why can software tests neither be conducted completely nor prove that software is error-free?

Answer 1

Software tests cannot be conducted completely due to the vast number of possible scenarios, nor can they prove the absence of errors. Each project requires individual decisions on the extent of resources spent on quality management.

Question 2

What are the two main components of the total costs of a software system?

Answer 2

The total costs consist of:

• Production costs: Costs for producing desired functions and functionality.
• Quality costs: Efforts for error prevention, detection, localization, and correction.

Question 3

What are the two categories of quality costs, and what do they include?

Answer 3

• Error Prevention Costs: Activities conducted before delivery to reduce post-delivery errors, including constructive and analytical quality management.
• Error Correction Costs: Costs incurred after delivery to localize and correct errors, including internal efforts (e.g., software tests after code modifications) and external penalties or reputational damage.

Question 4

What are external costs for error correction, and how can they affect a company?

Answer 4

External costs include contractual penalties and damages like customer dissatisfaction or reputational harm, which may lead to loss of confidence in the software manufacturer.

Question 5

How does the cost of error prevention relate to the quality level of a system?

Answer 5

The cost of error prevention increases disproportionately with higher quality levels. Early measures improve quality quickly, but diminishing returns occur as quality assurance intensifies.

Question 6

What happens to error correction costs in a largely untested system?

Answer 6

In largely untested systems, error correction costs are extremely high because errors are identified only after delivery. These costs decrease as the quality level of the system improves.

Question 7

What is the goal of quality cost optimization in software projects?

Answer 7

The goal is to balance prevention and correction costs by aiming for optimal quality costs, preventing costly post-delivery errors without overspending on error prevention.

Question 8

What factors must be evaluated to plan cost-effective quality assurance measures?

Answer 8

1. Risks and their probabilities of occurrence.
2. Consequential costs of errors.
3. Project budget constraints.

These evaluations guide planning for the lowest possible quality assurance costs.