Q.10) When designing a dependable system, you therefore have to consider
Answers
Answer:
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Explanation:
Dependable systems are desirable since they are “trustworthy,” as discussed in the security communities and reliable engineering communities. Dependable systems are typically characterized by the the following attributes:
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Reliability: the system behaves as expected, with very few errors.
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Availability: the system and services are mostly available, with very little or no down time.
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Safety: the systems do not pose unacceptable risks to the environment or the health of users.
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Confidentiality: data and other information should not be divulged without intent and authorization.
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Survivability: The system services should be robust enough to withstand accidents and attacks.
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Integrity: System data should not be modified without intent and authorization.
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Maintainability: Maintenance of system hardware and services should not be difficult or excessively expensive.
These attributes have some overlap among themselves. For example, just like security, it is a weakest link phenomenon, in that the strength of the whole is determined by the weakest link in the chain. Thus, for a product or system to be considered dependable, it should posses all the aforementioned attributes. Conversely, a system is not dependable in proportion to the degree of lack of these dependability attributes. In most cases, dependability is also not a binary phenomenon (present or absent) but based on gradations and acceptable thresholds. These thresholds are specific to infrastructures such as electronic, electromechanical, and quantum, as well as applications, such as communications, process control, and data processing.
Among the dependability attributes, some need to be emphasized over others in specific system applications. For example, in banking transactions, accuracy is crucial, and if accuracy cannot be guaranteed, the transaction must be aborted and rolled back. In contrast, sensors controlling a deep sea oil rig may be large in number, and the base station utilizes all the signals, including signals from malfunctioning sensors and a composite picture is constructed from all available data. Hundred percent accuracy can be sacrificed if sufficient degrees of availability, survivability, and maintainability are achieved within a budget threshold. Similarly, intelligence communications demand security and privacy but might not be that concerned with delays of the order of seconds or minutes.
One of the keys for dependable systems is that they should be empirically verifiable in terms of their dependability. That means that fashionable or trendy methodologies that may be very popular need to be objectively assessed on the basis of their true effectiveness. One of the measures for dependability is the number of faults. Faults are errors in design or implementation that cause failures. A failure is deemed to have occurred if any of the functional specifications of the system are not met. Failures can range from minor to catastrophic, depending upon the impact of failure on the system and the immediate environment. Minor failures are referred to as errors. The underlying faults may thus be prioritized, based on their potential impact. Lack of dependability means that the system is undependable due to shortcoming in one or more of the dependability attributes, caused by faults in the system and potential cause of system failure.
Faults can manifest themselves during the operation of a system. Such faults are known as active. Otherwise, the faults may be present and possibly manifest themselves in the future. Such faults are referred to as dormant, and the purpose of the testing phase in systems engineering is to discover as many dormant and active faults as possible before deployment and general use of the tested system.