112 research outputs found
Design, Implementation and Experiments for Moving Target Defense Framework
The traditional defensive security strategy for distributed systems employs well-established defensive techniques such as; redundancy/replications, firewalls, and encryption to prevent attackers from taking control of the system. However, given sufficient time and resources, all these methods can be defeated, especially when dealing with sophisticated attacks from advanced adversaries that leverage zero-day exploits
Methods for Structural Pattern Recognition: Complexity and Applications
Katedra kybernetik
Automatic error recovery for LR parsers in theory and practice
This thesis argues the need for good syntax error handling schemes in language
translation systems such as compilers, and for the automatic incorporation of such schemes
into parser-generators. Syntax errors are studied in a theoretical framework and practical
methods for handling syntax errors are presented.
The theoretical framework consists of a model for syntax errors based on the concept of
a minimum prefix-defined error correction,a sentence obtainable from an erroneous string by
performing edit operations at prefix-defined (parser defined) errors. It is shown that for an
arbitrary context-free language, it is undecidable whether a better than arbitrary choice of edit
operations can be made at a prefix-defined error. For common programming languages,it is
shown that minimum-distance errors and prefix-defined errors do not necessarily coincide,
and that there exists an infinite number of programs that differ in a single symbol only; sets
of equivalent insertions are exhibited.
Two methods for syntax error recovery are, presented. The methods are language
independent and suitable for automatic generation. The first method consists of two stages,
local repair followed if necessary by phrase-level repair. The second method consists of a
single stage in which a locally minimum-distance repair is computed. Both methods are
developed for use in the practical LR parser-generator yacc, requiring no additional
specifications from the user. A scheme for the automatic generation of diagnostic messages
in terms of the source input is presented. Performance of the methods in practice is evaluated
using a formal method based on minimum-distance and prefix-defined error correction. The
methods compare favourably with existing methods for error recovery
Recommended from our members
Proceedings of the Workshop on Membrane Computing, WMC 2016.
yesThis Workshop on Membrane Computing, at the Conference of Unconventional
Computation and Natural Computation (UCNC), 12th July 2016, Manchester,
UK, is the second event of this type after the Workshop at UCNC 2015 in
Auckland, New Zealand*. Following the tradition of the 2015 Workshop the
Proceedings are published as technical report.
The Workshop consisted of one invited talk and six contributed presentations
(three full papers and three extended abstracts) covering a broad spectrum of
topics in Membrane Computing, from computational and complexity theory to
formal verification, simulation and applications in robotics. All these papers â
see below, but the last extended abstract, are included in this volume.
The invited talk given by Rudolf Freund, âP SystemsWorking in Set Modesâ,
presented a general overview on basic topics in the theory of Membrane Computing
as well as new developments and future research directions in this area.
Radu Nicolescu in âDistributed and Parallel Dynamic Programming Algorithms
Modelled on cP Systemsâ presented an interesting dynamic programming
algorithm in a distributed and parallel setting based on P systems enriched with
adequate data structure and programming concepts representation. Omar Belingheri,
Antonio E. Porreca and Claudio Zandron showed in âP Systems with
Hybrid Setsâ that P systems with negative multiplicities of objects are less powerful
than Turing machines. Artiom Alhazov, Rudolf Freund and Sergiu Ivanov
presented in âExtended Spiking Neural P Systems with Statesâ new results regading
the newly introduced topic of spiking neural P systems where states are
considered.
âSelection Criteria for Statistical Model Checkerâ, by Mehmet E. Bakir and
Mike Stannett, presented some early experiments in selecting adequate statistical
model checkers for biological systems modelled with P systems. In âTowards
Agent-Based Simulation of Kernel P Systems using FLAME and FLAME GPUâ,
Raluca Lefticaru, Luis F. MacĂas-Ramos, IonuĆŁ M. Niculescu, LaurenĆŁiu MierlÄ
presented some of the advatages of implementing kernel P systems simulations in
FLAME. Andrei G. Florea and CÄtÄlin Buiu, in âAn Efficient Implementation and Integration of a P Colony Simulator for Swarm Robotics Applications" presented an interesting and efficient implementation based on P colonies for swarms of Kilobot robots.
*http://ucnc15.wordpress.fos.auckland.ac.nz/workshop-on-membrane-computingwmc-
at-the-conference-on-unconventional-computation-natural-computation
Fast Packet Processing on High Performance Architectures
The rapid growth of Internet and the fast emergence of new network applications have brought great challenges and complex issues in deploying high-speed and QoS guaranteed IP network. For this reason packet classication and network intrusion detection have assumed a key role in modern communication networks in order to provide Qos and security. In this thesis we describe a number of the most advanced solutions to these tasks. We introduce NetFPGA and Network Processors as reference platforms both for the design and the implementation of the solutions and
algorithms described in this thesis. The rise in links capacity reduces the time available to network devices for packet processing. For this reason, we show different solutions which, either by heuristic and randomization or by smart construction of state machine, allow IP lookup, packet classification and deep packet inspection to be fast in real devices based on high speed platforms such as NetFPGA or Network Processors
Integrated Data, Message, and Process Recovery for Failure Masking in Web Services
Modern Web Services applications encompass multiple distributed interacting components, possibly including millions of lines of code written in different programming languages. With this complexity, some bugs often remain undetected despite extensive testing procedures, and occasionally cause transient system failures. Incorrect failure handling in applications often leads to incomplete or to unintentional request executions. A family of recovery protocols called interaction contracts provides a generic solution to this problem by means of system-integrated data, process, and message recovery for multi-tier applications. It is able to mask failures, and allows programmers to concentrate on the application logic, thus speeding up the development process. This thesis consists of two major parts. The first part formally specifies the interaction contracts using the state-and-activity chart language. Moreover, it presents a formal specification of a concrete Web Service that makes use of interaction contracts, and contains no other error-handling actions. The formal specifications undergo verification where crucial safety and liveness properties expressed in temporal logics are mathematically proved by means of model checking. In particular, it is shown that each end-user request is executed exactly once. The second part of the thesis demonstrates the viability of the interaction framework in a real world system. More specifically, a cascadable Web Service platform, EOS, is built based on widely used components, Microsoft Internet Explorer and PHP application server, with interaction contracts integrated into them.Heutige Web-Service-Anwendungen setzen sich aus mehreren verteilten interagierenden
Komponenten zusammen. Dabei werden oft mehrere Programmiersprachen eingesetzt,
und der Quellcode einer Komponente kann mehrere Millionen Programmzeilen
umfassen. In Anbetracht dieser KomplexitÀt bleiben typischerweise einige
Programmierfehler trotz intensiver QualitÀtssicherung unentdeckt und verursachen
vorĂŒbergehende SystemsausfĂ€lle zur Laufzeit. Eine ungenĂŒgende Fehlerbehandlung in
Anwendungen fĂŒhrt oft zur unvollstĂ€ndigen oder unbeabsichtigt wiederholten
AusfĂŒhrung einer Operation. Eine Familie von Recovery-Protokollen, die so genannten
"Interaction Contracts", bietet eine generische Lösung dieses Problems. Diese Recovery-
Protokolle sorgen fĂŒr die Fehlermaskierung und ermöglichen somit, dass Entwickler ihre
ganze Konzentration der Anwendungslogik widmen können. Dies trÀgt zu einer
erheblichen Beschleunigung des Entwicklungsprozesses bei.
Diese Dissertation besteht aus zwei wesentlichen Teilen. Der erste Teil widmet sich der
formalen Spezifikation der Recovery-Protokolle unter Verwendung des Formalismus der
State-and-Activity-Charts. DarĂŒber hinaus entwickeln wir die formale Spezifikation einer
Web-Service-Anwendung, die auĂer den Recovery-Protokollen keine weitere
Fehlerbehandlung beinhaltet. Die formalen Spezifikationen werden in Bezug auf kritische
Sicherheits- und Lebendigkeitseigenschaften, die als temporallogische Formeln
angegeben sind, mittels "Model Checking" verifiziert. Unter anderem wird somit
mathematisch bewiesen, dass jede Operation eines Endbenutzers genau einmal ausgefĂŒhrt
wird. Der zweite Teil der Dissertation beschreibt die Implementierung der Recovery-
Protokolle im Rahmen einer beliebig verteilbaren Web-Service-Plattform EOS, die auf
weit verbreiteten Web-Produkten aufbaut: dem Browser "Microsoft Internet Explorer"
und dem PHP-Anwendungsserver
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