基于UML活动图化简方法的工作流模型校核研究

针对开放、响应型系统建模UML活动图表现优良的特性,UML活动图在工作流建模领域也引起了人们的极大关注。然而相关的研究仅仅起步,特别是针对相应的模型校核技术更是研究甚少。该文提出了基于UML活动图化简方法的工作流模型校核技术,在UML活动图到活动超图映射基础之上,对活动超图建立化简规则,通过化简实现工作流模型校核。实践证明此方法有效。     

一种用户行为模式的挖掘算法

最大频繁事件序列挖掘是数据挖掘中重要的研究课题之一。该文提出了一种新的挖掘用户行为模式的算法。该算法采用位图索引表的数据格式,使用一种有效的基于前缀树的频繁事件序列扩展方法,结合有效的剪枝技术,明显地加速了最大频繁事件序列的生成。     

一般k阶余因式的k超连接表达式和分解定理

本文应用有向超图理论提出了线性系统不定参数矩阵Y的一般k阶余因式Y(ii)的两个k超连接表达式,并根据它导出了Y(ii)的一个分解定理。应用该定理容易对任意线性大系统进行多层撕裂和分析。这是一种新的多层拓扑分析方法,它可以扩大一台计算机所能拓扑分析的系统规模。     

Network extraction from sandstone and carbonate pore space images

A methodology for extracting networks from pore space images is presented. It computes the location and sizes of pores and throats to create a topologically equivalent representation of the void space of three-dimensional (3D) rock images, using the concept of maximal balls [Silin, D.B., Jin, G. and Patzek, T.W., 2003. Robust Determination of the Pore Space Morphology in Sedimentary rocks. SPE 84296, Annual Technical Conference and Exhibition, Denver, Colorado, USA, October.]. The model is successfully tested on sandstone and carbonate samples. The network extracted from a representation of Fontainebleau sandstone yielded a coordination number distribution that agrees well with that computed using a different extraction algorithm that is based on knowing the location of grain centers [Øren, P. and Bakke, S., 2003. Reconstruction of Berea sandstone and pore-scale modelling of wettability effects. Journal of Petroleum Science and Engineering 39 177–199.]. The model was further tested on a carbonate sample from subsurface Oman for which it is not possible to identify grains easily. For all the samples investigated in this study, the predicted absolute permeabilities, using the newly extracted networks, agree well with the laboratory measured values.     

Analysis of the resequencing buffer in a homogeneous M/M/2 queue

The resequencing problem is encountered in many practical information systems such as distributed database and communication networks. In these systems customers, such as messages in a computer network, have to be delivered to users in their original order. Therefore, those customers which become out of order due to the randomness of the system are forced to wait in a resequencing buffer so that their delivered order can be guaranteed. The previous work on the resequencing problem mainly concentrated on the delay aspect. From both theoretical and practical viewpoints, however, the queue length characteristics of the resequencing buffer are also significant. We consider the queue length distribution of the resequencing buffer fed by a homogeneous M/M/2 queue. The exact analysis is carried out for the probability mass functions of the queue length in equilibrium and the maximal occupancy which corresponds to the queue length just before the departure instants of customers from the resequencing buffer.     

Characterization of a subclass of finite-dimensional estimation algebras with maximal rank application to filtering

Finite-dimensional estimation Lie algebras play a crucial role in the study of finite-dimensional filters for partially observed stochastic process. When the dynamics noise is Gaussian we can characterize the so-called estimation Lie algebras with maximal rank in terms of the observation functions (necessarily affine) and the drift (necessarily a sum of a skew-symmetric linear term and a gradient vector field, with a functional relationship), under the assumption that the estimation algebra has one and only one operator of order greater or equal to two in any of its basis.     

The derivation of on-line algorithms,with an application to finding palindromes

A theory for the derivation of on-line algorithms is presented. The algorithms are derived in the Bird-Meertens calculus for program transformations. This calculus provides a concise functional notation for algorithms, and a few powerful theorems for proving equalities of functions. The theory for the derivation of on-line algorithms is illustrated with the derivation of an algorithm for finding palindromes.An on-line linear-time random access machine (RAM) algorithm for finding the longest palindromic substring in a string is derived. For the purpose of finding the longest palindromic substring, all maximal palindromic substrings are computed. The list of maximal palindromes obtained in the computation of the longest palindrome can be used for other purposes such as finding the largest palindromic rectangle in a matrix and finding the shortest partition of a string into palindromes.This research was supported by the Dutch organization for scientific research NWO, under NFI project STOP, project number NF 62/63-518.     

A Distributed Algorithm for Determining Minimal Covers of Acyclic Database Schemes

Acyclic databases possess several desirable properties for their design and use.A distributed algorithm is proposed for determining a minimal cover of an alpha-,beta-,gamma-,or Berge-acyclic database scheme over a set of attributes in a distributed environment.     

关系数据库中MVD超图的讨论

本文提出了ＭＶＤ超图的概念，给出了正向ＭＶＤ超图、逆向ＭＶＤ超图的定义。深入讨论了逆向ＭＶＤ超图、逆向准路（结点）、可人发准路结点、不可分准路结点及最小不可分准路结点等。在此基础上，给出了求解最小不可分结点的闭包算法。     

Computations of probabilistic output admissible set for uncertain constrained systems

This paper considers uncertain constrained systems, and develops two algorithms for computing a probabilistic output admissible (POA) set which is a set of initial states probabilistically assured to satisfy the constraint. The first algorithm is inspired by an existing randomized sequential technique. The second algorithm alleviates the computational effort based on heuristics. The present algorithms terminate in a finite number of iterations and provide a POA set. Additionally, we can obtain information on the size of the resulting set a posteriori. A numerical simulation demonstrates the applicability of the POA set to a control system design scheme.