PhD ThesisModel-based speci cation languages provide a means for obtaining assurance of dependability
of complex computer-based systems, but provide little support for modelling and
analysing fault behaviour, which is inherently probabilistic in nature. In particular,
the need for a detailed account of the role of continuous probability has been largely
overlooked.
This thesis addresses the role of continuous probability in model-based speci cation
languages. A model-based speci cation language (sGCL) that supports continuous
probability distributions is de ned. The use of sGCL and how it interacts with engineering
practices is also explored. In addition, a re nement ordering for continuous
probability distributions is given, and the challenge of combining non-determinism and
continuous probability is discussed in depth.
The thesis is presented in three parts. The rst uses two case studies to explore the
use of probability in formal methods. The rst case study, on
ash memory, is used
to present the capabilities of probabilistic formal methods and to determine the kinds
of questions that require continuous probability distributions to answer. The second,
on an emergency brake system, illustrates the strengths and weaknesses of existing languages
and provides a basis for exploring a prototype language that includes continuous
probability.
The second part of the thesis gives the formal de nition of sGCL's syntax and semantics.
The semantics is made up of two parts, the proof theory (transformer semantics)
and the underpinning mathematics (relational semantics). The additional language
constructs and semantical features required to include non-determinism as well as continuous
probability are also discussed. The most challenging aspect lies in proving the
consistency of the semantics when non-determinism is also included.
The third part uses a nal case study, on an aeroplane pitch monitor, to demonstrate
the use of sGCL. The new analysis techniques provided by sGCL, and how they t in
with engineering practices, are explored.EPSRC:
The School of Computing Science, Newcastle University:
DEPLOY project