Dependable Systems

Question 1

Most important aspect of many systems

Answer 1

• Dependability of the system

Question 2

Dependable system

Answer 2

• Reliability
• Availability
• Security

Question 3

Hardware failure

Answer 3

• Hardware fails because of design and manufacturing errors, or because components have reached the end of their natural life.

Question 4

Software failure

Answer 4

• Software fails due to errors in its specification, design, or implementation.

Question 5

Operational failure

Answer 5

• Human operators make mistakes. This is now perhaps the largest single cause of system failures in sociotechnical systems.

Question 6

Redundancy

Answer 6

• The inclusion of spare capacity in a system that can be used in the event of failure of part of the system

Question 7

Diversity

Answer 7

• The use of different types of redundant components so that the probability of a common failure that affects all redundant components is reduced

Question 8

Formal methods

Answer 8

• Formal specification
• Specification analysis and proof
• Transformational development
• Program verification

Question 9

Verification-based approaches

Answer 9

• These are different representations of a software system such that a specification and a program implementing that specification are proved to be equivalent.
• This demonstrates the absence of implementation errors.

Question 10

Refinement-based approaches

Answer 10

• A representation of a system is systematically transformed into another, lower-level representation, e.g., a specification is transformed automatically into an implementation.
• This means that, if the transformation is correct, the representations are equivalent.

Question 11

Causes of failures

Answer 11

• Hardware
• Software
• Operational failure

Question 12

Dependability costs:

Answer 12

• Increase exponentially with dependability requirement.

Question 13

Holistic system design

Answer 13

• Interaction between all components and layers in a system

Question 14

Dependability process

Answer 14

• Explicitly defined
• Repeatable

Question 15

Formal methods

Answer 15

• Approaches to software development based on mathematical representation and analysis