L10 - Dependability

Question 1

Fault Types

Answer 1

1. time (transient, permanent, intermittent)
2. internal (physical, design)
3. external (physical, input data)

Question 2

Heisenbugs

Answer 2

software bug that seems to disappear or alter its behavior when one attempts to study it

Question 3

Fault Tolerance enables _________________. It requires ___________ and prior _____________.

Answer 3

Fault Tolerance enables the system to work in presence of faults. It requires fault detection and prior error specification.

Question 4

Which exceptions can be detected by the environment?

Answer 4

• synchronously raised exceptions (divide by zero)
• asynchronously raised exceptions (failure of health monitoring mechanism)

Question 5

Exceptions detected by application

Answer 5

• Synchronously raised (failure of a program check)
• asynchronously raised exceptions (process recognises error that leads to missing deadline)

Question 6

Error

Answer 6

wrong state in system

Question 7

Transient Fault

Answer 7

A transient fault starts at a particular time and remains in the system until it disappears.

Question 8

A permanent fault _______________ until _______________.

Answer 8

A permanent fault remains in the system until repaired.

Question 9

Intermittent Fault

Answer 9

An intermittent fault is defined as a transient fault that occurs sporadic from time to time.

Question 10

Impairments

Answer 10

Faults, Errors and Failures.

Question 11

Name three key requirements for attributes.

Answer 11

1. Availability (Readiness for Usage)
2. Reliability (Continuity of Service Delivery)
3. Safety (Non-Occurence Of Catastrophic Consequences)
4. Confidentiality (Non-Occurence of unauthorized disclosure)
5. Integrity (Non-Occurence of improper alteration of information)
6. Maintainability (Aptitude to undergo repairs or evolutions)

Question 12

Confidentiality

Answer 12

Confidentiality is the non-occurence of unauthorized disclosure.

Question 13

A test only shows _____________ of faults not their _____________.

Answer 13

A test only shows presence of faults not their absence.

Question 14

What activates an exception handler and with what is it associated with?

Answer 14

An exception handler gets activated with an exception and associated with a domain that specifies a region of computation. There may be several handlers for a particular exception.

Question 15

Decomposition is also known as ____________. How is it defined?

Answer 15

Decomposition is also known as Top Down Design. It is defined as the systematic breakdown of complex into smaller system. Isolated components can be understood and engineered as individuals.

Question 16

What is an alternative description of abstraction and whats the concept behind?

Answer 16

Abstraction (Bottom Up Design): detailed consideration of components.

Question 17

What is described by information hiding and how do you implement it in C?

Answer 17

Information hiding is the reduced visibility outside of the module. In C: .h-file contains an interface of module, .c-file contains body - no formal relationship.

Question 18

Name characteristics of Ada.

Answer 18

• planned to be mandatory for all DoD projects that include embedded systems
• latest version is Ada 2012^ block-structured language
• constructs control how tasks are dispatched
• consists out of subprogram/package/task/protected unit

Question 19

What is a disadvantage of C?

Answer 19

C does not provide native exception handling. This has to be implemented by the programmer.

Question 20

C is a _________________ and therefore provides _________________ without _________________.

Answer 20

C is a low level programming language and therefore provides structure and flexibility without complex language restrictions.

Question 21

Name an advantage and a problem that occurs while developing RTS in C++.

Answer 21

• Better software engineering practice because of encapsulation and more advanced level of abstraction as in C
• Lack of concurrent software with predictable timing behaviour makes it difficult to develop software for RTS.