Abstract:
A safety-critical system executes the critical tasks, the failure of which may
jeopardize human life, lead to considerable nancial misfortune, or cause extensive
environmental damage. Therefore, safety is considered as one of the most
critical areas of research, while dealing with safety-critical systems. Traditional
safety-critical systems are being converted into digital systems for several bene ts.
To support various features of a safety-critical system, the digital systems are
becoming more complex in functional behaviors. Complex digital systems comprised
of many software and hardware components mostly of them are heterogeneous
in nature. A safety-critical system comprises of a large no. of heterogeneous
components, there is higher risk always associated with the safety-critical systems
due to possible failures in Hardware/Software involved there in. Several techniques
are available to perform the safety analysis of such systems. An extensive literature
survey was carried out to identify the available methods for safety analysis of
safety-critical digital systems. Most of them works on qualitative assessment rather
than quantitative assessment. However, quantitative assessment has several bene ts
over qualitative assessment such as { (i) risks are sorted by their adversity impact,
and (ii) security levels can be better determined/de ned through consideration
of three elements that are availability, integrity, and con dentiality. Further,
safety analysis during the early phases of system development life cycle has many
signi cant bene ts such as { (i) help in taking decisions to select most suitable design (ii) cost minimization (iii) analyzing the sensitivity of the system safety to
its component safety (iv)identify safety bottlenecks. The proposed work deals with
a new probabilistic approach to quantify safety of safety-critical systems during the
design phase of the systems that is based on the probabilistic safety assessment to
deal with the shortcomings of the existing techniques using state-space models.
Further, it is a challenging task to capture all the requirements including safety
requirements through state space models. Also, verifying that the constructed
model has captured all the requirements is again a problem in itself, because of all
the understanding of stakeholders may not get captured during development of the
state-space model. Failing to model all the requirements will give inaccurate safety
assessment. UML is a well-known and successful way of modelling which is used
for specifying requirements. UML can capture all the requirements and be easily
understood by all the stakeholders. This motivates us to propose a methodology to
convert the UML model into a state space model that can be used for quantitative
assessment of a safety-critical systems under consideration. A framework is proposed
and introduced in this thesis to transform UML model into a state-space model in the
form of a Petri net, which is a reliable graphical and mathematical tool to perform
several static and dynamic analysis.
All the above proposed approaches are validated considering a real-time
safety-critical system of Nuclear Power Plant along with some noticeable ndings.
