19,058 research outputs found
Fifty years of Hoare's Logic
We present a history of Hoare's logic.Comment: 79 pages. To appear in Formal Aspects of Computin
Instruction sequences for the production of processes
Single-pass instruction sequences under execution are considered to produce
behaviours to be controlled by some execution environment. Threads as
considered in thread algebra model such behaviours: upon each action performed
by a thread, a reply from its execution environment determines how the thread
proceeds. Threads in turn can be looked upon as producing processes as
considered in process algebra. We show that, by apposite choice of basic
instructions, all processes that can only be in a finite number of states can
be produced by single-pass instruction sequences.Comment: 23 pages; acknowledgement corrected, reference update
The Sliding Window Protocol Revisited
We give a correctness proof of the sliding window protocol. Both safety and liveness properties are addressed. We show how faulty channels can be represented as nondeterministic programs. The correctness proof is given as a sequence of correctness-preserving transformations of a sequential program that satisfies the original specification, with the exception that it does not have any faulty channels. We work as long as possible with a sequential program, although the transformation steps are guided by the aim of going to a distributed program. The final transformation steps consist in distributing the actions of the sequential program over a number of processes
Automatic Probabilistic Program Verification through Random Variable Abstraction
The weakest pre-expectation calculus has been proved to be a mature theory to
analyze quantitative properties of probabilistic and nondeterministic programs.
We present an automatic method for proving quantitative linear properties on
any denumerable state space using iterative backwards fixed point calculation
in the general framework of abstract interpretation. In order to accomplish
this task we present the technique of random variable abstraction (RVA) and we
also postulate a sufficient condition to achieve exact fixed point computation
in the abstract domain. The feasibility of our approach is shown with two
examples, one obtaining the expected running time of a probabilistic program,
and the other the expected gain of a gambling strategy.
Our method works on general guarded probabilistic and nondeterministic
transition systems instead of plain pGCL programs, allowing us to easily model
a wide range of systems including distributed ones and unstructured programs.
We present the operational and weakest precondition semantics for this programs
and prove its equivalence
Distributed Verification of Rare Properties using Importance Splitting Observers
Rare properties remain a challenge for statistical model checking (SMC) due
to the quadratic scaling of variance with rarity. We address this with a
variance reduction framework based on lightweight importance splitting
observers. These expose the model-property automaton to allow the construction
of score functions for high performance algorithms.
The confidence intervals defined for importance splitting make it appealing
for SMC, but optimising its performance in the standard way makes distribution
inefficient. We show how it is possible to achieve equivalently good results in
less time by distributing simpler algorithms. We first explore the challenges
posed by importance splitting and present an algorithm optimised for
distribution. We then define a specific bounded time logic that is compiled
into memory-efficient observers to monitor executions. Finally, we demonstrate
our framework on a number of challenging case studies
Nondeterminism and Guarded Commands
The purpose of this paper is to discuss the relevance of nondeterminism in
computer science, with a special emphasis on Dijkstra's guarded commands
language.Comment: 34 pages. This is authors' version of Chapter 8 of the book K.R. Apt
and C.A.R. Hoare (editors), Edsger Wybe Dijkstra: His Life, Work, and Legacy,
volume 45 of ACM Books. ACM/Morgan & Claypool, 202
On the behaviours produced by instruction sequences under execution
We study several aspects of the behaviours produced by instruction sequences
under execution in the setting of the algebraic theory of processes known as
ACP. We use ACP to describe the behaviours produced by instruction sequences
under execution and to describe two protocols implementing these behaviours in
the case where the processing of instructions takes place remotely. We also
show that all finite-state behaviours considered in ACP can be produced by
instruction sequences under execution.Comment: 36 pages, consolidates material from arXiv:0811.0436 [cs.PL],
arXiv:0902.2859 [cs.PL], and arXiv:0905.2257 [cs.PL]; abstract and
introduction rewritten, examples and proofs adde
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