Managing the Evolution of Dependability Cases for Systems of Systems

. Dependability is a composite property consisting of attributes such as reliability,
availability, safety and security. The achievement of these attri~utes is often essential
for the operational success of systems undertaking critical and complex tasks.
.Assurance that the fmal system will demonstrate the required dependability qualities,
can be crucial to the acceptance of the system into service.
Safety cases are a well established c,oncept used to establish assurance about the safety
properties of a system. However, safety cases focus only on one attribute of
dependability. The principles and processes ofcreating an integrated dependability case
- that assures all aspects of dependable system behaviour - are less well understood. A
number of challenges are faced when attempting to support dependability case
development. These include the systematic elicitation of dependability goals, the
management and justification of trade-offs, and the evolution of multi-attribute
arguments in step with the design process.
This thesis addresses these challenges by defming a rigorous framework, accompanied
by a set of methods, for establishing dependability cases. Firstly, a method for eliciting
dependability requirements is defmed by extending existing safety deviational analysis
techniques. Secondly, a method for systematically identifying and managing justified
trade-offs is presented. Thirdly, the thesis describes the co-evolution of depen~bility .
case arguments alongside system development - using a dependability case architecture
that corresponds to system structures. Finally, the thesis unifies these contributions by
defming a metamodel that captures and interrelates the 'concepts underlying the
proposed methods. Evaluation of the work is presented by means of peer review, pilot
studies and industrial examples.