Journal of Computer and System Sciences (J Comput Syst Sci )


The Journal of Computer and System Sciences publishes original research papers in computer science and related subjects in system science, with attention to the relevant mathematical theory. Applications-oriented papers may also be accepted. Research Areas Include: Traditional Subjects such as: Theory of algorithms and computability; Formal languages; Automata theory; Contemporary Subjects such as Complexity theory Algorithmic; Complexity; Parallel and distributed computing; Computer networks; Neural networks; Computational learning theory; Database theory and practice Computer modeling of complex systems.

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  • Website
    Journal of Computer and System Sciences website
  • Other titles
    Journal of computer and system sciences (Online), Journal of computer and system sciences
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    Document, Periodical, Internet resource
  • Document type
    Internet Resource, Computer File, Journal / Magazine / Newspaper

Publications in this journal

  • [show abstract] [hide abstract]
    ABSTRACT: Belief revision has been extensively studied in the framework of propositional logic, but just recently revision within fragments of propositional logic has gained attention. Hereby it is not only the belief set and the revision formula which are given within a certain language fragment, but also the result of the revision has to be located in the same fragment. So far, research in this direction has been mainly devoted to the Horn fragment of classical logic. Here we present a general approach to define new revision operators derived from known operators, such that the result of the revision remains in the fragment under consideration. Our approach is not limited to the Horn case but applicable to any fragment of propositional logic where the models of the formulas are closed under a Boolean function. Thus we are able to uniformly treat cases as dual Horn, Krom and affine formulas, as well.
    Journal of Computer and System Sciences 01/2014; 80(2):427–449.
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    ABSTRACT: We prove a complexity dichotomy theorem for the most general form of Boolean #CSP where every constraint function takes values in the field of complex numbers CC. We first give a non-trivial tractable class of Boolean #CSP which was inspired by holographic reductions. The tractability crucially depends on algebraic cancelations which are absent for non-negative numbers. We then completely characterize all the tractable Boolean #CSP with complex-valued constraints and show that we have found all the tractable ones, and every remaining problem is #P-hard. We also improve our result by proving the same dichotomy theorem holds for Boolean #CSP with maximum degree 3 (every variable appears at most three times). The concept of Congruity and Semi-congruity provides a key insight and plays a decisive role in both the tractability and hardness proofs. We also introduce local holographic reductions as a technique in hardness proofs.
    Journal of Computer and System Sciences 01/2014; 80(1):217–236.
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    ABSTRACT: Delay tolerant networks (DTNs) are resource-constrained networks where messages are relayed in a store-carry-forward fashion. In most routing protocols of DTNs, each node is required to honestly relay messages. However, some nodes may violate this principle, and relay messages in a greedy way in order to maximize their own benefit, such as to get more transmission opportunities and more rewards, and to save their own resources. This greedy behavior breaks the routing fairness and decreases the message delivery ratio of DTNs. The existing security solutions in DTNs to address selfish behaviors and malicious attacks cannot cope with the greedy behavior because of the greedy nature of nodes. We propose a message matching-based detection (MMBD) method where a smart mobile trusted module (MTM) is introduced to prevent the greedy behavior. The MTM in each node honestly computes a forwarding sequence of messages buffered in the node when a connection opportunity is available. If the node misbehaves, the actual forwarding sequence of messages cannot match with the forwarding sequence of messages computed by the MTM, so the MTM doesn't sign these messages. Honest nodes refuse to receive messages without the MTM's signature. This method requires less computation time and fewer resources than the trusted computing group attestation. Furthermore, as shown in simulation results, this method can offer a fair routing environment for honest nodes in DTNs, and increases the average message delivery ratio of the network when the greedy behavior occurs.
    Journal of Computer and System Sciences 01/2014;
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    ABSTRACT: We define extensions of the full branching-time temporal logic CTL⁎ in which the path quantifiers are relativised by formal languages of infinite words, and consider its natural fragments obtained by extending the logics CTL and CTL+ in the same way. This yields a small and two-dimensional hierarchy of temporal logics parametrised by the class of languages used for the path restriction on one hand, and the use of temporal operators on the other. We motivate the study of such logics through two application scenarios: in abstraction and refinement they offer more precise means for the exclusion of spurious traces; and they may be useful in software synthesis where decidable logics without the finite model property are required. We study the relative expressive power of these logics as well as the complexities of their satisfiability and model-checking problems.
    Journal of Computer and System Sciences 01/2014; 80(2):375–389.
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    ABSTRACT: We describe the mechanisation of some foundational results in the theory of context-free languages (CFLs), using the HOL4 system. We focus on pushdown automata (PDAs). We show that two standard acceptance criteria for PDAs (“accept-by-empty-stack” and “accept-by-final-state”) are equivalent in power. We are then able to show that the pushdown automata (PDAs) and context-free grammars (CFGs) accept the same languages by showing that each can emulate the other. With both of these models to hand, we can then show a number of basic, but important results. For example, we prove the basic closure properties of the context-free languages such as union and concatenation. Along the way, we also discuss the varying extent to which textbook proofs (we follow Hopcroft and Ullman) and our mechanisations diverge: sometimes elegant textbook proofs remain elegant in HOL; sometimes the required mechanisation effort blows up unconscionably.
    Journal of Computer and System Sciences 01/2014; 80(2):346–362.
  • Journal of Computer and System Sciences 01/2014; 80(2):321–322.
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    ABSTRACT: The displacement calculus of Morrill, Valentín and Fadda (2011) [25] aspires to replace the calculus of Lambek (1958) [13] as the foundation of categorial grammar by accommodating intercalation as well as concatenation while remaining free of structural rules and enjoying Cut-elimination and its good corollaries. Jäger (2005) [11] proposes a type logical treatment of anaphora with syntactic duplication using limited contraction. Morrill and Valentín (2010) [24] apply (modal) displacement calculus to anaphora with lexical duplication and propose extension with a negation as failure in conjunction with additives to capture binding conditions. In this paper we present an account of anaphora developing characteristics and employing machinery from both of these proposals.
    Journal of Computer and System Sciences 01/2014; 80(2):390–409.
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    ABSTRACT: Discovering frequent factors from long strings is an important problem in many applications, such as biosequence mining. In classical approaches, the algorithms process a vast database of small strings. However, in this paper we analyze a small database of long strings. The main difference resides in the high number of patterns to analyze. To tackle the problem, we have developed a new algorithm for discovering frequent factors in long strings. We present an Apriori-like solution which exploits the fact that any super-pattern of a non-frequent pattern cannot be frequent. The SANSPOS algorithm does a multiple-pass, candidate generation and test approach. Multiple length patterns can be generated in a pass. This algorithm uses a new data structure to arrange nodes in a trie. A Positioning Matrix is defined as a new positioning strategy. By using Positioning Matrices, we can apply advanced prune heuristics in a trie with a minimal computational cost. The Positioning Matrices let us process strings including Short Tandem Repeats and calculate different interestingness measures efficiently. Furthermore, in our algorithm we apply parallelism to transverse different sections of the input strings concurrently, speeding up the resulting running time. The algorithm has been successfully used in natural language and biological sequence contexts.
    Journal of Computer and System Sciences 01/2014; 80(1):3–15.
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    ABSTRACT: Recently proposed formal reliability analysis techniques have overcome the inaccuracies of traditional simulation based techniques but can only handle problems involving discrete random variables. In this paper, we extend the capabilities of existing theorem proving based reliability analysis by formalizing several important statistical properties of continuous random variables like the second moment and the variance. We also formalize commonly used concepts about the reliability theory such as survival, hazard, cumulative hazard and fractile functions. With these extensions, it is now possible to formally reason about important measures of reliability (the probabilities of failure, the failure risks and the mean-time-to failure) associated with the life of a system that operates in an uncertain and harsh environment and is usually continuous in nature. We illustrate the modeling and verification process with the help of examples involving the reliability analysis of essential electronic and electrical system components.
    Journal of Computer and System Sciences 01/2014; 80(2):323–345.
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    ABSTRACT: This paper proposes an efficient broadcast encryption scheme for key distribution in MANET. No message exchange is required to establish a group key. The communication overhead remains unchanged as group size grows. In order for the group member to obtain session key, only one bilinear pairing computation is required. The proposal is also evaluated through efficiency, security analysis and comparison with other existing schemes. We test the efficiency of the scheme on a modern station through simulation. The performance analysis shows its suitability for large scale MANETs. It is shown that the new scheme is provable secure in standard model. The comparison indicates that this scheme has efficiency surpassing congeneric schemes. Furthermore, an improved scheme against chosen ciphertext attack (CCA) is proposed in order to enhance the security. Thus, the proposal in this paper can not only meet security demands but is also efficient in terms of computation and communication.
    Journal of Computer and System Sciences 01/2014; 80(3):533–545.
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    ABSTRACT: The ranking of interval-valued intuitionistic fuzzy sets (IVIFSs) is very important for the interval-valued intuitionistic fuzzy decision making. From the probability viewpoint, the possibility degree of comparison between two interval-valued intuitionistic fuzzy numbers (IVIFNs) is defined by using the notion of 2-dimensional random vector, and a new method is then developed to rank IVIFNs. Hereby the ordered weighted average operator and hybrid weighted average operator for IVIFNs are defined based on the Karnik–Mendel algorithms and employed to solve multi-attribute group decision making problems with IVIFNs. The individual overall attribute values of alternatives are obtained by using the weighted average operator for IVIFNs. By using the hybrid weighted average operator for IVIFNs, we can obtain the collective overall attribute values of alternatives, which are used to rank the alternatives. A numerical example is examined to illustrate the effectiveness and flexibility of the proposed method in this paper.
    Journal of Computer and System Sciences 01/2014; 80(1):237–256.
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    ABSTRACT: MapReduce is regarded as an adequate programming model for large-scale data-intensive applications. The Hadoop framework is a well-known MapReduce implementation that runs the MapReduce tasks on a cluster system. G-Hadoop is an extension of the Hadoop MapReduce framework with the functionality of allowing the MapReduce tasks to run on multiple clusters in a Grid environment. However, G-Hadoop simply reuses the user authentication and job submission mechanism of Hadoop, which is designed for a single cluster and hence does not suit for the Grid environment. This work proposes a new security model for G-Hadoop. The security model is based on several security solutions such as public key cryptography and the SSL protocol, and is dedicatedly designed for distributed environments like the Grid. This security framework simplifies the users authentication and job submission process of the current G-Hadoop implementation with a single-sign-on approach. In addition, the designed security framework provides a number of different security mechanisms to protect the G-Hadoop system from traditional attacks as well as abusing and misusing.
    Journal of Computer and System Sciences 01/2014;
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    ABSTRACT: We solve systems of boolean implicit equations and relations with union and complementation. If the languages are regular, we determine whether a system of implicit boolean equations or relations has solutions. If there is a solution, we provide an effective construction of a (regular) solution. We give representations for maximal and minimal solutions. Moreover, we also solve the problem of uniqueness of solutions as well as whether infinitely many solutions exist.
    Journal of Computer and System Sciences 01/2014; 80(2):457–467.
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    ABSTRACT: An inherent feature of IP addresses is the aliasing that arises due to dynamic address allocation. This creates a significant barrier to the estimation of the malicious host population from a set of intrusion alerts. In this paper, we propose a method for estimating the number of malicious hosts that may have bound to an alerted address, based on the correlation of different data sets that were collected independently and a probabilistic model of host-to-address bindings. We analysed a two week trace of real-world intrusion alerts along with a global survey of ping responses, and inferred that over 80% of malicious addresses were bound to multiple hosts. Such aliasing effects highlight the inaccuracy of assuming static bindings between hosts and addresses when exact host identification is not possible due to privacy protection. However, our method demonstrates that reliable inferences can still be made when a sufficient overlap exists between the correlated data sets.
    Journal of Computer and System Sciences 01/2014; 80(3):502–519.
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    ABSTRACT: We present the first implementation of a distributed clock generation scheme for Systems-on-Chip that recovers from an unbounded number of arbitrary transient faults despite a large number of arbitrary permanent faults. We devise self-stabilizing hardware building blocks and a hybrid synchronous/asynchronous state machine enabling metastability-free transitions of the algorithm's states. We provide a comprehensive modeling approach that permits to prove, given correctness of the constructed low-level building blocks, the high-level properties of the synchronization algorithm (which have been established in a more abstract model). We believe this approach to be of interest in its own right, since this is the first technique permitting to mathematically verify, at manageable complexity, high-level properties of a fault-prone system in terms of its very basic components. We evaluate a prototype implementation, which has been designed in VHDL, using the Petrify tool in conjunction with some extensions, and synthesized for an Altera Cyclone FPGA.
    Journal of Computer and System Sciences 01/2014; 80(4):860–900.

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