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  • 期刊名称:

    Informatic Record

  • 中文名称: 信息学报
  • 刊频: 0.923
  • ISSN: 0001-5903
  • 出版社: -
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  • 机译 通过平价博弈从LTL规范实际合成反应系统
    摘要: The synthesis of reactive systems from linear temporal logic (LTL) specifications is an important aspect in the design of reliable software and hardware. We present our adaption of the classic automata-theoretic approach to LTL synthesis, implemented in the tool Strix which has won the two last synthesis competitions (Syntcomp2018/2019). The presented approach is (1) structured, meaning that the states used in the construction have a semantic structure that is exploited in several ways, it performs a (2) forward exploration such that it often constructs only a small subset of the reachable states, and it is (3) incremental in the sense that it reuses results from previous inconclusive solution attempts. Further, we present and study different guiding heuristics that determine where to expand the on-demand constructed arena. Moreover, we show several techniques for extracting an implementation (Mealy machine or circuit) from the witness of the tree-automaton emptiness check. Lastly, the chosen constructions use a symbolic representation of the transition functions to reduce runtime and memory consumption. We evaluate the proposed techniques on the Syntcomp2019 benchmark set and show in more detail how the proposed techniques compare to the techniques implemented in other leading LTL synthesis tools.
  • 机译 GR(1)合成的性能启发式算法和相关算法
    摘要: Reactive synthesis for the GR(1) fragment of LTL has been implemented and studied in many works. In this work we present and evaluate a list of heuristics to potentially reduce running times for GR(1) synthesis and related algorithms. The list includes several heuristics for controlled predecessor computation and BDDs, early detection of fixed-points and unrealizability, fixed-point recycling, and several heuristics for unrealizable core computations. We have implemented the heuristics and integrated them in our synthesis environment Spectra Tools, a set of tools for writing specifications and running synthesis and related analyses. We evaluate the presented heuristics on SYNTECH15, a total of 78 specifications of 6 autonomous Lego robots, on SYNTECH17, a total of 149 specifications of 5 autonomous Lego robots, all written by 3rd year undergraduate computer science students in two project classes we have taught, as well as on benchmarks from the literature. The evaluation investigates not only the potential of the suggested heuristics to improve computation times, but also the difference between existing benchmarks and the robot's specifications in terms of the effectiveness of the heuristics. Our evaluation shows positive results for the application of all the heuristics together, which get more significant for specifications with slower original running times. It also shows differences in effectiveness when applied to different sets of specifications. Furthermore, a comparison between Spectra, with all the presented heuristics, and two existing tools, RATSY and Slugs, over two well-known benchmarks, shows that Spectra outperforms both on most of the specifications; the larger the specification, the faster Spectra becomes relative to the two other tools.
  • 机译 渴望策略懒惰综合的一种符号算法
    摘要: We present an algorithm for solving two-player safety games that combines a mixed forward/backward search strategy with a symbolic representation of the state space. By combining forward and backward exploration, our algorithm can synthesize strategies that are eager in the sense that they try to prevent progress towards the error states as soon as possible, whereas standard backwards algorithms often produce permissive solutions that only react when absolutely necessary. We provide experimental results for two classes of crafted benchmarks, the benchmark set of the Reactive Synthesis Competition (SYNTCOMP) 2017, as well as a set of randomly generated benchmarks. The results show that our algorithm in many cases produces more eager strategies than a standard backwards algorithm, and solves a number of benchmarks that are intractable for existing tools. Finally, we observe a connection between our algorithm and a recently proposed algorithm for the synthesis of controllers that are robust against disturbances, pointing to possible future applications.
  • 机译 具有线性时序逻辑规范最大可靠性的反应性合成
    摘要: A challenging problem for autonomous systems is to synthesize a reactive controller that conforms to a set of given correctness properties. Linear temporal logic (LTL) provides a formal language to specify the desired behavioral properties of systems. In applications in which the specifications originate from various aspects of the system design, or consist of a large set of formulas, the overall system specification may be unrealizable. Driven by this fact, we develop an optimization variant of synthesis from LTL formulas, where the goal is to design a controller that satisfies a set of hard specifications and minimally violates a set of soft specifications. To that end, we introduce a value function that, by exploiting the LTL semantics, quantifies the level of violation of properties. Inspired by the idea of bounded synthesis, we fix a bound on the implementation size and search for an implementation that is optimal with respect to the said value function. We propose a novel maximum satisfiability encoding of the search for an optimal implementation (within the given bound on the implementation size). We iteratively increase the bound on the implementation size until a termination criterion, such as a threshold over the value function, is met.
  • 机译 从超特性综合
    摘要: We study the reactive synthesis problem for hyperproperties given as formulas of the temporal logic HyperLTL. Hyperproperties generalize trace properties, i.e., sets of traces, to sets of sets of traces. Typical examples are information-flow policies like noninterference, which stipulate that no sensitive data must leak into the public domain. Such properties cannot be expressed in standard linear or branching-time temporal logics like LTL, CTL, or CTL*\documentclass[12pt]. Furthermore, HyperLTL subsumes many classical extensions of the LTL realizability problem, including realizability under incomplete information, distributed synthesis, and fault-tolerant synthesis. We show that, while the synthesis problem is undecidable for full HyperLTL, it remains decidable for the there exists*\documentclass[12pt], fragments. Beyond these fragments, the synthesis problem immediately becomes undecidable. For universal HyperLTL, we present a semi-decision procedure that constructs implementations and counterexamples up to a given bound. We report encouraging experimental results obtained with a prototype implementation on example specifications with hyperproperties like symmetric responses, secrecy, and information flow.
  • 机译 谓词编程:交互式综合的形式模型
    摘要: Program synthesis is the problem of computing from a specification a program that implements it. New and popular variations on the synthesis problem accept specifications in formats that are easier for the human synthesis user to provide: input-output example pairs, type information, and partial logical specifications. These are all partial specification formats, encoding only a fraction of the expected behavior of the program, leaving many matching programs. This transition into partial specification also changes the mode of work for the user, who now provides additional specifications until they are happy with the synthesis result. Therefore, synthesis becomes an iterative, interactive process. We present a formal model for interactive synthesis, parameterized by an abstract domain of predicates on programs. The abstract domain is used to describe both the iterative refinement of the specifications and reduction of the candidate program space. We motivate the need for a general feedback model via predicates by showing that examples, the most frequent specification tool, are an insufficient tool to differentiate between programs, even when used as a full specification. We use the formal model to describe the behavior of several real-world synthesizers. Additionally, we present two conditions for termination of a synthesis session, one hinging only on the properties of the available partial specifications, and the other also on the behavior of the user. Finally, we show conditions for realizability of the user's intent, and show the limitations of backtracking when it is apparent a session will fail.
  • 机译 综合最佳弹性控制器
    摘要: Recently, Dallal, Neider, and Tabuada studied a generalization of the classical game-theoretic model used in program synthesis, which additionally accounts for unmodeled intermittent disturbances. In this extended framework, one is interested in computing optimally resilient strategies, i.e., strategies that are resilient against as many disturbances as possible. Dallal, Neider, and Tabuada showed how to compute such strategies for safety specifications. In this work, we compute optimally resilient strategies for a much wider range of winning conditions and show that they do not require more memory than winning strategies in the classical model. Our algorithms only have a polynomial overhead in comparison to the ones computing winning strategies. In particular, for parity conditions, optimally resilient strategies are positional and can be computed in quasipolynomial time.
  • 机译 用于连续工厂的可证明安全的数字控制器的自动化形式综合
    摘要: We present a sound and automated approach to synthesizing safe, digital controllers for physical plants represented as time-invariant models. Models are linear differential equations with inputs, evolving over a continuous state space. The synthesis precisely accounts for the effects of finite-precision arithmetic introduced by the controller. The approach uses counterexample-guided inductive synthesis: an inductive generalization phase produces a controller that is known to stabilize the model but that may not be safe for all initial conditions of the model. Safety is then verified via bounded model checking: if the verification step fails, a counterexample is provided to the inductive generalization, and the process further iterates until a safe controller is obtained. We demonstrate the practical value of this approach by automatically synthesizing safe controllers for physical plant models from the digital control literature.
  • 机译 使用无离散多分辨率抽象的渐进稳定开关系统的安全综合
    摘要: Control of continuous and hybrid systems using discrete abstractions often suffers from scalability issues, due to the use of state space partitions as symbolic states. In this paper, for incrementally stable switched systems, we introduce a class of abstractions that do not rely on state space partitions but use mode sequences as symbolic states. Our approach differs from existing works by the possibility of considering sequences of varying length, giving the possibility to adjust locally the resolution of the abstraction. Temporal constraints on the switching signal can also be taken into account. We thus define multi-resolution bisimilar abstractions that enjoy interesting properties that can be used to design specific algorithms to synthesize safety controllers. These algorithms need not compute the full abstraction that is built incrementally during controller synthesis, exploring finer resolutions only when the specification cannot be enforced at the coarser level. We illustrate the approach by a numerical example inspired by road traffic regulation.
  • 机译 对称网络中自稳定协议的参数化综合
    摘要: Self-stabilization in distributed systems is a technique to guarantee convergence to a set of legitimate states without external intervention when a transient fault or bad initialization occurs. Recently, there has been a surge of efforts in designing techniques for automated synthesis of self-stabilizing algorithms that are correct by construction. Most of these techniques, however, are not parameterized, meaning that they can only synthesize a solution for a fixed and predetermined number of processes. In this paper, we report a breakthrough in parameterized synthesis of self-stabilizing algorithms in symmetric networks, including ring, line, mesh, and torus. First, we develop cutoffs that guarantee (1) closure in legitimate states, and (2) deadlock-freedom outside the legitimate states. We also develop a sufficient condition for convergence in self-stabilizing systems. Since some of our cutoffs grow with the size of the local state space of processes, scalability of the synthesis procedure is still a problem. We address this problem by introducing a novel SMT-based technique for counterexample-guided synthesis of self-stabilizing algorithms in symmetric networks. We have fully implemented our technique and successfully synthesized solutions to maximal matching, three coloring, and maximal independent set problems for ring and line topologies.
  • 机译 可用通道:网络设计的动态,行为和效率
    摘要:We present a simple model, called depleatable channels, of multi-hop communication in ad hoc networks. We introduce a model for channel energy consumption, and we propose a notion of channel equivalence based on the communication service they provide, regardless of specific routing protocols. In particular, we consider equivalent two channels with identical maximum and minimum inhibiting flow, and prove that this notion of equivalence, and variants of it, coincide with standard equivalences borrowed from the theory of concurrency. Unfortunately, while the maximum flow can be computed in polynomial time, calculating the value of a minimum inhibiting flow is NP-hard. Thus, we propose a characterization of those graphs, called weak, which admit charge assignments for which the minimum inhibiting flow is strictly less than the maximum flow and show that weakness can be checked efficiently by providing an algorithm that does so in polynomial time.
  • 机译 加权迭代线性控制
    摘要:We combine three extensions of context-free grammars: (a) associating its nonterminals with storage configurations, (b)equipping its rules with weights, and (c) controlling its derivations. For a commutative semiring K, we introduce the class of weighted languages generated by K-weighted linear context-free grammars with storage S and with derivations controlled by (S,K)-recognizable weighted languages. The control on the derivations can be iterated in a natural way. We characterize the n-th iteration of the control in terms of the n-th iteration of the one-turn pushdown operator on the storage S of the control weighted language. Moreover, for each proper semiring we prove that iterating the control yields an infinite, strict hierarchy of classes of weighted languages.
  • 机译 不断更新的红黑树
    摘要:We show how a few modifications to the red-black trees allow for constant worst-case update time (once the position of the element to be inserted or deleted is known). The resulting structure is based on relaxing some of the properties of the red-black trees while guaranteeing that the height remains logarithmic with respect to the number of nodes. Compared to the other search trees with constant worst-case update time, our tree is the first to provide a tailored deletion procedure without using the global rebuilding technique. In addition, our procedures are simpler and allow for an easier proof of correctness than those alternative trees.
  • 机译 基于Paxos的算法可最大程度地减少共识过程恢复的开销
    摘要:Consensus is a fundamental abstraction in distributed systems and its solvability is widely discussed in the literature. In message passing distributed systems where there is a need to solve sequential instances of consensus, it is possible that some processes become faulty during one instance and recover later in another instance. Though consensus algorithms should be equipped both to handle process failures and process recovery, only a little amount of work has been done in the literature to handle process recovery. Handling process recovery is not trivial because a recovered process may broadcast a new message which could hamper the progress made by other processes towards achieving consensus in their current round, and thereby forcing them to start a new round. Therefore algorithms that are not designed to handle process recovery require O(f) rounds or O(f) time to achieve consensus, where at most f processes can recover and is the message delay in the system. But Dutta et al. (in: International conference on dependable systems and networks (DSN'05), pp 22-27), 2005. 10.1109/DSN.2005.54) showed that the overhead of handling process recovery is constant and their algorithm takes 17 time to achieve consensus. In this work, we introduce a new Paxos based algorithm that lowers the upper bound to 11. We also show that if all process failures are initial, the upper bound can be further reduced to 5. Our algorithm selectively enables processes executing lower rounds to decide irrespective of the presence of higher rounds in the system, minimizing the effect of recovered processes starting a higher round.
  • 机译 关于过渡系统中多面体不变量存在的可判定性
    摘要:Automated program verification often proceeds by exhibiting inductive invariants entailing the desired properties. For numerical properties, a classical class of invariants is convex polyhedra: solution sets of system of linear (in)equalities. Forty years of research on convex polyhedral invariants have focused, on the one hand, on identifying easier subclasses, on the other hand on heuristics for finding general convex polyhedra. These heuristics are however not guaranteed to find polyhedral inductive invariants when they exist. To our best knowledge, the existence of polyhedral inductive invariants has never been proved to be undecidable. In this article, we show that the existence of convex polyhedral invariants is undecidable, even if there is only one control state in addition to the bad one. The question is still open if one is not allowed any nonlinear constraint.
  • 机译 使用静态和动态切入点的程序Petri网模型的等效性检查
    摘要:Extensive optimizing and parallelizing transformations are carried out on programs, both by (untrusted) compilers and human experts, before deploying them on some platform architecture which is by and large parallel. It is therefore important to devise some suitable modelling paradigm which is capable of capturing parallelism in such a way that proving equivalence of the source programs and their transformed versions becomes easier. In the present work, an untimed Petri net model with data constraints, called CPN model (Coloured Petri net), is used to model the parallel behaviours. Being value based, such models depict more vividly the data dependencies which lie at the core of such transformations; accordingly, they are likely to provide more suitable internal representations (IRs) of both the source and the transformed programs than the IRs like sequential control flow graphs (CFGs). A path based equivalence checking method for CPN models with rigorous treatment of the complexity and correctness issues have been presented. Experimental results show the effectiveness of the approach.
  • 机译 接口自动机,组件兼容性和错误的广义理论
    摘要:Interface theories allow system designers to reason about the composability and compatibility of concurrent system components. Such theories often extend both de Alfaro and Henzinger's Interface Automata and Larsen's Modal Transition Systems, which leads, however, to several issues that are undesirable in practice: an unintuitive treatment of specified unwanted behaviour, a binary compatibility concept that does not scale to multi-component assemblies, and compatibility guarantees that are insufficient for software product lines. In this article we show that communication mismatches are central to all these problems and, thus, the ability to represent such errors semantically is an important feature of an interface theory. Accordingly, we present the error-aware interface theory EMIA, where the above shortcomings are remedied by introducing explicit fatal error states. In addition, we prove via a Galois insertion that EMIA is a conservative generalisation of the established Modal Interface Automata theory.
  • 机译 在路径控制的插入删除系统上
    摘要:A graph-controlled insertion-deletion system is a regulated extension of an insertion-deletion system. It has several components and each component contains some insertion-deletion rules. These components are the vertices of a directed control graph. A transition is performed by any applicable rule in the current component on a string and the resultant string is then moved to the target component specified in the rule. This also describes the arcs of the control graph. Starting from an axiom in the initial component, strings thus move through the control graph. The language of the system is the set of all terminal strings collected in the final component. In this paper, we investigate a variant of the main question in this area: which combinations of size parameters (the maximum number of components, the maximal length of the insertion string, the maximal length of the left context for insertion, the maximal length of the right context for insertion; plus three similar restrictions with respect to deletion) are sufficient to maintain computational completeness of such restricted systems under the additional restriction that the (undirected) control graph is a path? Notice that these results also bear consequences for the domain of insertion-deletion P systems, improving on a number of previous results from the literature, concerning in particular the number of components (membranes) that are necessary for computational completeness results.
  • 机译 在模糊程序图上对模糊CTL进行符号检查
    摘要:Few fuzzy temporal logics and modeling formalisms are developed such that their model checking is both effective and efficient. State-space explosion makes model checking of fuzzy temporal logics inefficient. That is because either the modeling formalism itself is not compact, or the verification approach requires an exponentially larger yet intermediate representation of the modeling formalism. To exemplify, Fuzzy Program Graph (FzPG) is a very compact, and powerful formalism to model fuzzy systems; yet, it is required to be translated into an equal Fuzzy Kripke model with an exponential blow-up should it be formally verified. In this paper, we introduce Fuzzy Computation Tree Logic (FzCTL) and its direct symbolic model checking over FzPG that avoids the aforementioned state-space explosion. Considering compactness and readability of FzPG along with expressiveness of FzCTL, we believe the proposed method is applicable in real-world scenarios. Finally, we study formal verification of fuzzy flip-flops to demonstrate capabilities of the proposed method.
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