ECET 2026 SE – Software Quality: Reliability & Metrics

In ECET 2026, Software Engineering (SE) questions often focus on Software Quality, especially Reliability and Metrics. These are easy and direct concepts where formula-based questions frequently appear.

📘 Concept Notes

🔹 What is Software Quality?

The degree to which a software product meets specified requirements and user expectations.
Quality covers: correctness, reliability, usability, efficiency, maintainability, portability.

🔹 Software Reliability

Reliability = Probability that a software will work correctly for a specified time in a given environment.
Important for mission-critical systems (banking, healthcare, aerospace).

Factors affecting reliability:

Fault density (bugs per KLOC).
Testing coverage.
Complexity of design.

🔹 Reliability Metrics

Mean Time Between Failures (MTBF):

$MTBF = MTTF + MTTR$

$MTTF$ = Mean Time To Failure (average time software runs before failure).
$MTTR$ = Mean Time To Repair (average time to fix the failure).

Failure Rate (λ):

$\lambda = \dfrac{1}{MTTF}$

Reliability Function:

For time $t$ , reliability is:

$R(t) = e^{-\lambda t}$

Defect Density:

$Defect ; Density = \dfrac{\text{Number of Defects}}{\text{KLOC (Kilo Lines of Code)}}$

🔹 Software Metrics

Size Metrics: LOC, Function Points.
Complexity Metrics: Cyclomatic complexity.
Quality Metrics: Reliability, defect density.
Process Metrics: Effort, productivity.

📐 Example

A software has $MTTF = 200 ; \text{hours}$ and $MTTR = 20 ; \text{hours}$ .

$MTBF = 200 + 20 = 220 ; \text{hours}$

Failure Rate = $\lambda = \dfrac{1}{200} = 0.005$ per hour.

Reliability after 50 hours = $R(50) = e^{-0.005 \times 50} = e^{-0.25} \approx 0.7788$ .

🔟 10 Expected MCQs – ECET 2026

Q1. Software Reliability refers to:
A) Speed of execution
B) Probability of failure-free operation
C) Amount of memory used
D) Time to market

Q2. MTBF is:
A) Time between two tests
B) MTTF + MTTR
C) Only MTTF
D) Only MTTR

Q3. If MTTF = 100 hr and MTTR = 10 hr, MTBF = ?
A) 90 hr
B) 100 hr
C) 110 hr
D) 120 hr

Q4. Failure Rate (λ) is given by:
A) λ = MTTF × MTTR
B) λ = 1/MTTF
C) λ = MTTF/MTTR
D) λ = MTTR/MTTF

Q5. Reliability function is:
A) R(t) = e^(-λt)
B) R(t) = λ × t
C) R(t) = MTBF/t
D) R(t) = 1 – λt

Q6. Defect Density formula is:
A) Defects / KLOC
B) KLOC / Defects
C) Defects × KLOC
D) KLOC²

Q7. High MTBF means:
A) Less reliability
B) More reliability
C) More complexity
D) Less maintainability

Q8. Cyclomatic complexity is a type of:
A) Size metric
B) Complexity metric
C) Process metric
D) Quality metric

Q9. If a program has 20 defects in 10 KLOC, defect density = ?
A) 2
B) 0.2
C) 200
D) 20

Q10. Which is NOT a software quality metric?
A) Reliability
B) Defect Density
C) Cyclomatic Complexity
D) Compiler Speed

✅ Answer Key

Q.No	Answer
Q1	B
Q2	B
Q3	C
Q4	B
Q5	A
Q6	A
Q7	B
Q8	B
Q9	A
Q10	D

🧠 Explanations

Q1 → B: Reliability = probability of failure-free operation.
Q2 → B: MTBF = MTTF + MTTR.
Q3 → C: 100 + 10 = 110.
Q4 → B: Failure rate = 1/MTTF.
Q5 → A: Standard reliability function.
Q6 → A: Defects divided by KLOC.
Q7 → B: Higher MTBF → more reliability.
Q8 → B: Cyclomatic complexity measures logical complexity.
Q9 → A: 20/10 = 2 defects/KLOC.
Q10 → D: Compiler speed is not a software quality metric.

🎯 Why Practice Matters

Questions on MTBF, Reliability function, and Defect Density are direct and scoring.
These topics are common in both academic exams and interviews.
Simple formulas help you gain 2–3 sure marks in ECET SE section.

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Day 44 – Evening Session: Software Engineering – Software Quality: Reliability & Metrics – ECET 2026