9,955 research outputs found
Machine-Checked Proofs For Realizability Checking Algorithms
Virtual integration techniques focus on building architectural models of
systems that can be analyzed early in the design cycle to try to lower cost,
reduce risk, and improve quality of complex embedded systems. Given appropriate
architectural descriptions, assume/guarantee contracts, and compositional
reasoning rules, these techniques can be used to prove important safety
properties about the architecture prior to system construction. For these
proofs to be meaningful, each leaf-level component contract must be realizable;
i.e., it is possible to construct a component such that for any input allowed
by the contract assumptions, there is some output value that the component can
produce that satisfies the contract guarantees. We have recently proposed (in
[1]) a contract-based realizability checking algorithm for assume/guarantee
contracts over infinite theories supported by SMT solvers such as linear
integer/real arithmetic and uninterpreted functions. In that work, we used an
SMT solver and an algorithm similar to k-induction to establish the
realizability of a contract, and justified our approach via a hand proof. Given
the central importance of realizability to our virtual integration approach, we
wanted additional confidence that our approach was sound. This paper describes
a complete formalization of the approach in the Coq proof and specification
language. During formalization, we found several small mistakes and missing
assumptions in our reasoning. Although these did not compromise the correctness
of the algorithm used in the checking tools, they point to the value of
machine-checked formalization. In addition, we believe this is the first
machine-checked formalization for a realizability algorithm.Comment: 14 pages, 1 figur
The JKind Model Checker
JKind is an open-source industrial model checker developed by Rockwell
Collins and the University of Minnesota. JKind uses multiple parallel engines
to prove or falsify safety properties of infinite state models. It is portable,
easy to install, performance competitive with other state-of-the-art model
checkers, and has features designed to improve the results presented to users:
inductive validity cores for proofs and counterexample smoothing for test-case
generation. It serves as the back-end for various industrial applications.Comment: CAV 201
Towards Realizability Checking of Contracts using Theories
Virtual integration techniques focus on building architectural models of
systems that can be analyzed early in the design cycle to try to lower cost,
reduce risk, and improve quality of complex embedded systems. Given appropriate
architectural descriptions and compositional reasoning rules, these techniques
can be used to prove important safety properties about the architecture prior
to system construction. Such proofs build from "leaf-level" assume/guarantee
component contracts through architectural layers towards top-level safety
properties. The proofs are built upon the premise that each leaf-level
component contract is realizable; i.e., it is possible to construct a component
such that for any input allowed by the contract assumptions, there is some
output value that the component can produce that satisfies the contract
guarantees. Without engineering support it is all too easy to write leaf-level
components that can't be realized. Realizability checking for propositional
contracts has been well-studied for many years, both for component synthesis
and checking correctness of temporal logic requirements. However, checking
realizability for contracts involving infinite theories is still an open
problem. In this paper, we describe a new approach for checking realizability
of contracts involving theories and demonstrate its usefulness on several
examples.Comment: 15 pages, to appear in NASA Formal Methods (NFM) 201
Verifying the Safety of a Flight-Critical System
This paper describes our work on demonstrating verification technologies on a
flight-critical system of realistic functionality, size, and complexity. Our
work targeted a commercial aircraft control system named Transport Class Model
(TCM), and involved several stages: formalizing and disambiguating requirements
in collaboration with do- main experts; processing models for their use by
formal verification tools; applying compositional techniques at the
architectural and component level to scale verification. Performed in the
context of a major NASA milestone, this study of formal verification in
practice is one of the most challenging that our group has performed, and it
took several person months to complete it. This paper describes the methodology
that we followed and the lessons that we learned.Comment: 17 pages, 5 figure
Type-Based Termination, Inflationary Fixed-Points, and Mixed Inductive-Coinductive Types
Type systems certify program properties in a compositional way. From a bigger
program one can abstract out a part and certify the properties of the resulting
abstract program by just using the type of the part that was abstracted away.
Termination and productivity are non-trivial yet desired program properties,
and several type systems have been put forward that guarantee termination,
compositionally. These type systems are intimately connected to the definition
of least and greatest fixed-points by ordinal iteration. While most type
systems use conventional iteration, we consider inflationary iteration in this
article. We demonstrate how this leads to a more principled type system, with
recursion based on well-founded induction. The type system has a prototypical
implementation, MiniAgda, and we show in particular how it certifies
productivity of corecursive and mixed recursive-corecursive functions.Comment: In Proceedings FICS 2012, arXiv:1202.317
Model checking probabilistic and stochastic extensions of the pi-calculus
We present an implementation of model checking for probabilistic and stochastic extensions of the pi-calculus, a process algebra which supports modelling of concurrency and mobility. Formal verification techniques for such extensions have clear applications in several domains, including mobile ad-hoc network protocols, probabilistic security protocols and biological pathways. Despite this, no implementation of automated verification exists. Building upon the pi-calculus model checker MMC, we first show an automated procedure for constructing the underlying semantic model of a probabilistic or stochastic pi-calculus process. This can then be verified using existing probabilistic model checkers such as PRISM. Secondly, we demonstrate how for processes of a specific structure a more efficient, compositional approach is applicable, which uses our extension of MMC on each parallel component of the system and then translates the results into a high-level modular description for the PRISM tool. The feasibility of our techniques is demonstrated through a number of case studies from the pi-calculus literature
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