Software-Reliability

Question 1

The following table shoes the time between failures for a software system



The reliability of the system for one hour of operation assuming an exponential model is

A
0.45
B
0.63
C
0.84
D
0.95
Question 1 Explanation: 
MIBF = ∑(Start of downtime - Start of uptime)/No. of failures
MIBF = (6+4+8+5+6)/5 = 29/5
The probability or reliability that the product will work for a defined period of time without failure is given by
R(T) = exp(-T/MTBF); T = 1 hour
R(1) = e(-1/(29/5)) = e(-5/29) = 0.84
Question 2
A Design concept Refinement is a
A
Top-down approach
B
Complementary of Abstraction concept
C
Process of elaboration
D
All of the above
Question 2 Explanation: 
In the software engineering context, design concept is a top down approach which focuses on four major areas of concern: data, architecture, interfaces, and components.
The ​ data design t ​ ransforms the information domain model created during analysis into the data structures that will be required to implement the software.
The ​ architectural design d ​ efines the relationship between major structural elements of the software.
The ​ interface design d ​ escribes how the software communicates within itself, with systems that interoperate with it, and with humans who use it.
The ​ component-level design t ​ ransforms structural elements of the software architecture into a procedural description of software components.
Hence we can say that design concept is ​ Complementary of Abstraction concept and is a Process of elaboration.
Question 3
Consider a software program that is artificially seeded with 100 faults. While testing this program, 159 faults are detected, out of which 75 faults are from those artificially seeded faults. Assuming that both real and seeded faults are of same nature and have same distribution, the estimated number of undetected real faults is ______.
A
28
B
175
C
56
D
84
Question 3 Explanation: 
Total faults detected = 159
Real faults detected among all detected faults = 159 - 75 = 84
Since probability distribution is same, total number of real faults is (100/75)*84 = 112
Undetected real faults = 112- 84 = 28
There are 3 questions to complete.

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