120 research outputs found
RoBuSt: A Crash-Failure-Resistant Distributed Storage System
In this work we present the first distributed storage system that is provably
robust against crash failures issued by an adaptive adversary, i.e., for each
batch of requests the adversary can decide based on the entire system state
which servers will be unavailable for that batch of requests. Despite up to
crashed servers, with constant and
denoting the number of servers, our system can correctly process any batch of
lookup and write requests (with at most a polylogarithmic number of requests
issued at each non-crashed server) in at most a polylogarithmic number of
communication rounds, with at most polylogarithmic time and work at each server
and only a logarithmic storage overhead.
Our system is based on previous work by Eikel and Scheideler (SPAA 2013), who
presented IRIS, a distributed information system that is provably robust
against the same kind of crash failures. However, IRIS is only able to serve
lookup requests. Handling both lookup and write requests has turned out to
require major changes in the design of IRIS.Comment: Revised full versio
Allen Linear (Interval) Temporal Logic --Translation to LTL and Monitor Synthesis--
The relationship between two well established formalisms for temporal reasoning is first investigated, namely between Allen's interval algebra (or Allen's temporal logic, abbreviated \ATL) and linear temporal logic (\LTL). A discrete variant of \ATL is defined, called Allen linear temporal logic (\ALTL), whose models are \omega-sequences of timepoints, like in \LTL. It is shown that any \ALTL formula can be linearly translated into an equivalent \LTL formula, thus enabling the use of \LTL techniques and tools when requirements are expressed in \ALTL. %This translation also implies the NP-completeness of \ATL satisfiability. Then the monitoring problem for \ALTL is discussed, showing that it is NP-complete despite the fact that the similar problem for \LTL is EXPSPACE-complete. An effective monitoring algorithm for \ALTL is given, which has been implemented and experimented with in the context of planning applications
Weak Singular Hybrid Automata
The framework of Hybrid automata, introduced by Alur, Courcourbetis,
Henzinger, and Ho, provides a formal modeling and analysis environment to
analyze the interaction between the discrete and the continuous parts of
cyber-physical systems. Hybrid automata can be considered as generalizations of
finite state automata augmented with a finite set of real-valued variables
whose dynamics in each state is governed by a system of ordinary differential
equations. Moreover, the discrete transitions of hybrid automata are guarded by
constraints over the values of these real-valued variables, and enable
discontinuous jumps in the evolution of these variables. Singular hybrid
automata are a subclass of hybrid automata where dynamics is specified by
state-dependent constant vectors. Henzinger, Kopke, Puri, and Varaiya showed
that for even very restricted subclasses of singular hybrid automata, the
fundamental verification questions, like reachability and schedulability, are
undecidable. In this paper we present \emph{weak singular hybrid automata}
(WSHA), a previously unexplored subclass of singular hybrid automata, and show
the decidability (and the exact complexity) of various verification questions
for this class including reachability (NP-Complete) and LTL model-checking
(PSPACE-Complete). We further show that extending WSHA with a single
unrestricted clock or extending WSHA with unrestricted variable updates lead to
undecidability of reachability problem
Partially Ordered Two-way B\"uchi Automata
We introduce partially ordered two-way B\"uchi automata and characterize
their expressive power in terms of fragments of first-order logic FO[<].
Partially ordered two-way B\"uchi automata are B\"uchi automata which can
change the direction in which the input is processed with the constraint that
whenever a state is left, it is never re-entered again. Nondeterministic
partially ordered two-way B\"uchi automata coincide with the first-order
fragment Sigma2. Our main contribution is that deterministic partially ordered
two-way B\"uchi automata are expressively complete for the first-order fragment
Delta2. As an intermediate step, we show that deterministic partially ordered
two-way B\"uchi automata are effectively closed under Boolean operations.
A small model property yields coNP-completeness of the emptiness problem and
the inclusion problem for deterministic partially ordered two-way B\"uchi
automata.Comment: The results of this paper were presented at CIAA 2010; University of
Stuttgart, Computer Scienc
B\"uchi Complementation and Size-Change Termination
We compare tools for complementing nondeterministic B\"uchi automata with a
recent termination-analysis algorithm. Complementation of B\"uchi automata is a
key step in program verification. Early constructions using a Ramsey-based
argument have been supplanted by rank-based constructions with exponentially
better bounds. In 2001 Lee et al. presented the size-change termination (SCT)
problem, along with both a reduction to B\"uchi automata and a Ramsey-based
algorithm. The Ramsey-based algorithm was presented as a more practical
alternative to the automata-theoretic approach, but strongly resembles the
initial complementation constructions for B\"uchi automata. We prove that the
SCT algorithm is a specialized realization of the Ramsey-based complementation
construction. To do so, we extend the Ramsey-based complementation construction
to provide a containment-testing algorithm. Surprisingly, empirical analysis
suggests that despite the massive gap in worst-case complexity, Ramsey-based
approaches are superior over the domain of SCT problems. Upon further analysis
we discover an interesting property of the problem space that both explains
this result and provides a chance to improve rank-based tools. With these
improvements, we show that theoretical gains in efficiency of the rank-based
approach are mirrored in empirical performance
Consistency of service composition
We address the problem of ensuring that, when an application executing a service binds to a service that matches required functional properties, both the application and the service can work together, i.e., their composition is consistent. Our approach is based on a component algebra for service-oriented computing in which the configurations of applications and of services are modelled as asynchronous relational nets typed with logical interfaces. The techniques that we propose allow for the consistency of composition to be guaranteed based on properties of service orchestrations (implementations) and interfaces that can be checked at design time, which is essential for supporting the levels of dynamicity required by run-time service binding. © 2012 Springer-Verlag Berlin Heidelberg
Simulation Subsumption in Ramsey-Based Büchi Automata Universality and Inclusion Testing
International audienc
Antichain Algorithms for Finite Automata
We present a general theory that exploits simulation relations on transition systems to obtain antichain algorithms for solving the reachability and repeated reachability problems. Antichains are more succinct than the sets of states manipulated by the traditional fixpoint algorithms. The theory justifies the correctness of the antichain algorithms, and applications such as the universality problem for finite automata illustrate efficiency improvements. Finally, we show that new and provably better antichain algorithms can be obtained for the emptiness problem of alternating automata over finite and infinite words
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