39154147
Translating a Continuous-Time Temporal Logic into Timed Automata
LTLC is a continuous-time linear temporal logic for the specification of real-time systems. It can express both real-time systems and their properties. With LTLC, real-time systems can be described at different levels of abstraction, from high-level requirement specifications to low-level implementation models, and the conformance between different descriptions can be expressed by logical implication. The full logic of LTLC is undecidable. This paper will show that the existentially quantified fragment of LTLC is decidable. We achieve this goal by showing that the fragment can be translated into timed automata. Because the emptiness problem for timed automata is decidable, we then get a decision procedure for satisfiability for this fragment. This decidable part of LTLC is quite expressive. Many important real-time properties, such as bounded-response and bounded-invariance properties, can be expressed in it. The translation also enables us to develop a decision procedure for model checking real-time systems with quantifier-free LTLC specifications.
2186483
Improvements for the Symbolic Verification of Timed Automata
Based on the equivalence relation for location based reachability between continuous and integer semantics of closed timed automata, Beyer et al. have implemented the verifier Rabbit, with the uniform representation of reachable configurations. However, the growth of maximal constant of clock variables will decline the performance of Rabbit. The paper proposes an improved symbolic method, using binary decision diagrams (BDDs) to store the symbolic representation of discretized states, for the verification of timed systems. Compared with Rabbit, experiments demonstrate that besides the memory reduction, our implementation is also less sensitive to the size of clock domain.
31540088
Analyzing iKP Security in Applied Pi Calculus
The security for electronic payments is very important in electronic commerce. Many electronic payment protocols have been proposed recently to meet the security requirements. Since the design of a protocol is a difficult and error-prone task, the use of formal methods that allow for the verification of such protocols has received increasing attention. In this paper we take a look at the iKP from the point of view of the applied pi calculus. The iKP is described in the calculus and some security properties, mainly the authentication and anonymity properties, are verified.
6029798
Efficient Holistic Twig Joins in Leaf-to-Root Combining with Root-to-Leaf Way
Finding all the occurrences of a twig pattern on multiple elements in an XML document is a core operation for efficient evaluation of XML queries. Holistic twig join algorithms, TwigStack and TSGeneric, have been recognized as optimal solutions when the twig pattern only involves A-D(ancestordescendant) relationships, while iTwigJoin can be optimal for partial twig patterns that contain A-D only or P-C (parent-child) only relationships. However, existing algorithms involve unnecessary computations and CPU cost of them can be further improved, and we in this paper mainly address this problem. We first propose three effective optimization rules to avoid those unnecessary computations, and then present two algorithms incorporated with these optimization rules to effectively answer twig patterns in leaf-to-root combining with root-to-leaf way. Experimental results on various datasets indicate that our algorithms perform significantly better than existing proposals.
9766004
A PTAS for Minimizing Total Completion Time of Bounded Batch Scheduling
We consider a batch processing system {pi : i = 1, 2,..., n} where pi is the processing time of job i, and up to B jobs can be processed together such that the handling time of a batch is the longest processing time among jobs in the batch. The number of job types m is not fixed and all the jobs are released at the same time. Jobs are executed nonpreemptively. Our objective is to assign jobs to batches and sequence the batches so as to minimize the total completion time. The best previously known result is a 2-approximation algorithm due to D. S. Hochbaum and D. Landy [6]. In this paper, we establish the first polynomial time approximation scheme (PTAS) for the problem.
5926837
Composite Subscriptions in Content-Based Publish/Subscribe Systems
Distributed publish/subscribe systems are naturally suited for processing events in distributed systems. However, support for expressing patterns about distributed events and algorithms for detecting correlations among these events are still largely unexplored. Inspired from the requirements of decentralized, event-driven workflow processing, we design a subscription language for expressing correlations among distributed events. We illustrate the potential of our approach with a workflow management case study. The language is validated and implemented in PADRES. In this paper we present an overview of PADRES, highlighting some of its novel features, including the composite subscription language, the coordination patterns, the composite event detection algorithms, the rule-based router design, and a detailed case study illustrating the decentralized processing of workflows. Our experimental evaluation shows that rule-based brokers are a viable and powerful alternative to existing, special-purpose, content-based routing algorithms. The experiments also show that the use of composite subscriptions in PADRES significantly reduces the load on the network. Complex workflows can be processed in a decentralized fashion with a gain of 40% in message dissemination cost. All processing is realized entirely in the publish/subscribe paradigm.
11626813
Sorting Signed Permutations by Fixed-length Reversals
A signed n-permutation is a permutation on {1,2,…,n} in which each element is labelled by a positive or negative sign. Here we consider the problem of sorting signed permutations by fixed-length reversals. Indeed, limiting the transformations to reversals of length exactly k can be very restrictive, for example, (+1,+3,+2,+4,…,+n) can never be sorted to (+1,+2,+3,+4,…,+n) by 2-reversals. That is, for given two signed permutations it is not obvious whether they can be sorted to each other by k-reversals. Thus in 1996, Chen and Skiena gave the following open problem: what is the connectedness of signed permutations under fixed-length reversals? In this paper, we resolve this open problem when "fixed-length" is even, and give a characterization of the connectedness of signed n-permutations under 2l-reversal, for both linear and circular permutations.