The Power of Proofs: New Algorithms for Timed Automata Model Checking (with Appendix)

This paper presents the first model-checking algorithm for an expressive modal mu-calculus over timed automata, $L^{\mathit{rel}, \mathit{af}}_{\nu,\mu}$, and reports performance results for an implementation. This mu-calculus contains extended time-modality operators and can express all of TCTL. Our algorithmic approach uses an "on-the-fly" strategy based on proof search as a means of ensuring high performance for both positive and negative answers to model-checking questions. In particular, a set of proof rules for solving model-checking problems are given and proved sound and complete; we encode our algorithm in these proof rules and model-check a property by constructing a proof (or showing none exists) using these rules. One noteworthy aspect of our technique is that we show that verification performance can be improved with \emph{derived rules}, whose correctness can be inferred from the more primitive rules on which they are based. In this paper, we give the basic proof rules underlying our method, describe derived proof rules to improve performance, and compare our implementation of this model checker to the UPPAAL tool.Comment: This is the preprint of the FORMATS 2014 paper, but this is the full version, containing the Appendix. The final publication is published from Springer, and is available at http://link.springer.com/chapter/10.1007%2F978-3-319-10512-3_9 on the Springer webpag

An Incremental Approach to AbstractionCarrying Code

Abstract. Abstraction-Carrying Code (ACC) has recently been proposed as a framework for Proof-Carrying Code (PCC) in which the code model of the program) whose validity entails compliance with a predefined safety policy. Existing approaches for PCC are developed under the assumption that the consumer reads and validates the entire program w.r.t. the full certificate at once, in a non incremental way. In the context of ACC, we propose an incremental approach to PCC for the generation of certificates and the checking of untrusted updates of a (trusted) program, i.e., when a producer provides a modified version of a previously validated program. Our proposal is that, if the consumer keeps the original (fixed-point) abstraction, it is possible to provide only the program updates and the incremental certificate (i.e., the difference of abstractions). Furthermore, it is now possible to define an incremental checking algorithm which, given the new updates and its incremental certificate, only re-checks the fixpoint for each procedure affected by the updates and the propagation of the effect of these fixpoint changes. As a consequence, both certificate transmission time and checking time can be reduced significantly.

The Antiviral Activities and Mechanisms of Marine Polysaccharides: An Overview

Recently, the studies on the antiviral activities of marine natural products, especially marine polysaccharides, are attracting more and more attention all over the world. Marine-derived polysaccharides and their lower molecular weight oligosaccharide derivatives have been shown to possess a variety of antiviral activities. This paper will review the recent progress in research on the antiviral activities and the mechanisms of these polysaccharides obtained from marine organisms. In particular, it will provide an update on the antiviral actions of the sulfated polysaccharides derived from marine algae including carrageenans, alginates, and fucans, relating to their structure features and the structure–activity relationships. In addition, the recent findings on the different mechanisms of antiviral actions of marine polysaccharides and their potential for therapeutic application will also be summarized in detail

An Incremental Bisimulation Algorithm

Abstract. The notion of bisimulation has been used in various fields including Modal Logic, Set theory, Formal Verification, and XML indexing. In this paper we present the first algorithm for incremental maintenance of maximum bisim-ulation relation of a graph with respect to changes in the graph. Given a graph, its maximum bisimulation relation, and the changes in the graph, we determine the maximum bisimulation relation with respect to the changed graph by com-puting the changes in the given bisimulation relation. When the change in the graph induces small changes in the maximum bisimulation relation, our incre-mental algorithm is able to update the bisimulation relation on average an order of magnitude faster than the fastest available non-incremental algorithm. Prelim-inary experiments demonstrate the effectiveness of our algorithm. Our algorithm finds extensive use in verification where the specification changes over time, and XML indexing in database where the index structure, obtained by bisimulation on XML graph structure, needs to be maintained with respect to changes in the XML documents.