带有时钟变量的线性时序逻辑与实时系统验证

为了描述实时系统的性质和行为,10多年来,各种不同的时序逻辑,如Timed Computation Tree Logic,Metric Interval Temporal Logic和Real-Time Temporal Logic等相继提出来.这些时序逻辑适于表示实时系统的性质和规范,但不适于表示实时系统的实现模型.这样,在基于时序逻辑的实时系统的研究中,系统的性质和实现通常是用两种不同的语言来表示的.定义了一个带有时钟变量的线性时序逻辑(linear temporal logic with clocks,简称LTLC).它是由Manna和Pnueli提出的线性时序逻辑在实时情况下的一个推广.LTLC既能表示实时系统的性质,又能很方便地表示实时系统的实现.它能在统一的语义框架中表示出从高级的需求规范到低级的实现模型之间的不同抽象层次上的系统描述,并且能用逻辑蕴涵来表示不同抽象层次的系统描述之间的语义一致性.LTLC的这个特点将有助于实时系统的性质验证和实时系统的逐步求精.     

Application of a cellular automaton to simulations of granular flow in silos

A cellular automaton based on a gas model of hydrodynamics was used to calculate the kinematics of non-cohesive granular materials during confined flow in a mass flow and funnel flow model silo. In the model, collisions of particles were taken into account during granular flow. In addition, a simplified automaton was used wherein granular flow was assumed as an upward propagation of holes through a lattice composed of cells representing single particles. The advantages and disadvantages of both cellular automata were outlined.     

New Techniques for Regular Expression Searching

We present two new techniques for regular expression searching and use them to derive faster practical algorithms. Based on the specific properties of Glushkov’s nondeterministic finite automaton construction algorithm, we show how to encode a deterministic finite automaton (DFA) using O(m2^m) bits, where m is the number of characters, excluding operator symbols, in the regular expression. This compares favorably against the worst case of O(m2^m|Σ|) bits needed by a classical DFA representation (where Σ is the alphabet) and O(m2^2m) bits needed by the Wu and Manber approach implemented in Agrep. We also present a new way to search for regular expressions, which is able to skip text characters. The idea is to determine the minimum length ℓ of a string matching the regular expression, manipulate the original automaton so that it recognizes all the reverse prefixes of length up to ℓ of the strings originally accepted, and use it to skip text characters as done for exact string matching in previous work. We combine these techniques into two algorithms, one able and one unable to skip text characters. The algorithms are simple to implement, and our experiments show that they permit fast searching for regular expressions, normally faster than any existing algorithm.     

New Techniques for Regular Expression Searching

We present two new techniques for regular expression searching and use them to derive faster practical algorithms. Based on the specific properties of Glushkovs nondeterministic finite automaton construction algorithm, we show how to encode a deterministic finite automaton (DFA) using O(m2^m) bits, where m is the number of characters, excluding operator symbols, in the regular expression. This compares favorably against the worst case of O(m2^m||) bits needed by a classical DFA representation (where is the alphabet) and O(m2^2m) bits needed by the Wu and Manber approach implemented in Agrep. We also present a new way to search for regular expressions, which is able to skip text characters. The idea is to determine the minimum length of a string matching the regular expression, manipulate the original automaton so that it recognizes all the reverse prefixes of length up to of the strings originally accepted, and use it to skip text characters as done for exact string matching in previous work. We combine these techniques into two algorithms, one able and one unable to skip text characters. The algorithms are simple to implement, and our experiments show that they permit fast searching for regular expressions, normally faster than any existing algorithm.     

交互复杂度--面向网络计算的复杂度指标

随着网络计算的盛行,计算问题的解决越来越倾向于通过分布在网络上的服务的交互来完成,研究问题在交互意义上的复杂度显得日益重要．提出了以交互为基本要素的通用计算模型——交互积,在此基础上提出了算法的交互复杂度指标,并初步探索了交互复杂度和时间复杂度之间的关系．利用3-GIP的通用性,可以降低网格系统的成本和提高好用性,而交互复杂度可以作为网格上问题解决方案的评价指标,从而可以指导网格应用的开发．     

Decomposing a kind of weakly invertible finite automata with delay 2

Some properties of a finite automaton composed of two weakly invertible finite automata with delay 1 are given,where each of those two automata has the output set of each state with the same size.And for a weakly invertible finite automaton M with delay 2 satisfying the properties mentioned in this paper,two weakly invertible finite automata with delay 1 are constructed such that M is equivalent to a sub-finite-automaton of the composition of those two.So a method to decompose this a kind of weakly invertible finite automate with delay 2 is presented.     

Characterizations for the regular prefix codes and related families

Intrinsic characterizations by means of analogues of regular expressions are given for six families of regular languages related to the prefix codes, namely their reversals and their closure under union, the right and left ideals, and their complements. First, a characterization for the regular prefix codes is obtained, which is then used to characterize the other families. Characterizations by finite automata are also presented.This research has been sponsored in part by FINEP, CNPq and Canadian NRC.     

Codeterministic automata on infinite words

We prove that any recognizable set of infinite words is the infinite behaviour of some finite codeterministic automaton.     

Sorted dependency insertion grammars

An enhanced generative formalism is proposed based on the combination of two features: contextual derivation (as in Marcus contextual grammars) and sorted dependency structures (as in dependency grammars). The model is related to a variant of restarting automaton with rewriting and deletion. Preliminary results on the generative power as well as closure and decidability properties of the new model are presented.     

Remove Irrelevant Atomic Formulas for Timed Automaton Model Checking

Most of the timed automata reachability analysis algorithms in the literature explore the state spaces by enumeration of symbolic states, which use time constraints to represent a set of concrete states. A time constraint is a conjunction of atomic formulas which bound the differences of clock values. In this paper, it is shown that some atomic formulas of symbolic states generated by the algorithms can be removed to improve the model checking time- and space-efficiency. Such atomic formulas are called as irrelevant atomic formulas. A method is also presented to detect irrelevant formulas based on the test-reset information about clock variables. An optimized model-checking algorithm is designed based on these techniques. The case studies show that the techniques presented in this paper significantly improve the space- and time-efficiency of reachability analysis.