一种基于入侵检测的数据库安全审计

数据库审计是数据库安全的重要组成部分.它包括了日志记录和日志分析两个部分.然而传统的数据库审计系统往往只是一个简单的日志系统,而并不具备对日志进行分析的能力.即使存在审计分析能力,也往往具有语义不足,不易定义的特点.DBIDAUD模型使用入侵检测方法来实现数据库的审计分析能力,在DBIDAUD模型中存在一个规则库,其中定义了入侵检测知识,审计员通过定制规则库来定制系统的安全策略.模型具有丰富的语义和较高的效率,能够用来实现高安全数据库的审计系统.国产OSCARSEC安全数据库使用DBIDAUD实现了审计中心子系统.满足了国家安全标准四级的要求,在航天内部得到了充分的应用.     

A useful data-structuring technique

A data-structuring technique is described which enables data of widely varying types to be stored in a simple tree structure, and which requires only the name of a variable for both its type and value to be retrieved. The method uses well-established list-processing concepts in an unusual environment and illustrates the advantages to be gained by their use in application-oriented software. It has been used with some success in a modular processor for the storage of geometric and other data but is equally applicable to other fields.     

A parallel Householder tridiagonalization stratagem using scattered square decomposition

The parallel stratagem in this paper uses scattered square decomposition, introduced by G. Fox, for its data assignment and then exploits parallelism in the solution steps of the sequential Householder tridiagonalization algorithm. One may condense a real symmetric full matrix A of order n into a tridiagonal form by the stratagem in concurrent machines where N(= D²) processors are used. Expressions for efficiency and speedup are given for the evaluation of the stratagem. An alternative stratagem which requires less data transmission but more computations is also discussed. The results shown that the Householder Method of tridiagonalization may be implemented on a concurrent machine efficiently by scattered square decomposition provided that the number of matrix elements contained in each processor is much larger than the number of processors of the concurrent machine, and the ratio of the time to transmit one data item from one processor to any other processor to the time to perform a floating-point arithmetic operation is small enough.     

Goedel语言类型系统

Goedel语言是一种说明性逻辑程序设计语言。该语言基于一阶逻辑，引入了一个多态多类的类型系统和多种新的语言成分，支持抽象数据类型和模块化程序设计等技术，语言本身也具有很强的说明性语义。详细介绍了Goedel语言的类型系统及其构造，对在逻辑程序设计语言中引入类型系统的作用进行了一些深入的分析和讨论。     

Adaptive wormhole routing in k-ary n-cubes

Distributed memory multiprocessor (DMMP) systems have gained much attention because their performance can be easily scaled up by increasing the number of processor-memory modules. The k-ary n-cube is the most popular interconnection network topology currently used in DMMPs. Wormhole routing is one of the most promising switching technology and has been used in many new generation multicomputers. Wormhole routing makes the communication latency insensitive to the network diameter and reduces the size of the channel buffer of each router. The concept of virtual channels and virtual networks are widely invented for deadlock-free design. A fully adaptive wormhole routing method for k-ary n-cubes has been proposed by Linder in 1991 [10]. Unfortunately, the need of 2^{n − 1} virtual networks makes it unreasonable. In this paper, we propose a virtual network system to support an adaptive, minimal and deadlock free routing in k-ary n-cubes. It uses only four virtual networks but can get a higher degree of adaptability and higher traffic capacity. Simulation results are presented to verify the performance.     

用Sieve实现邮件过滤

Sieve是一种用来产生电子邮件过滤器的语言。为便于广大用户的使用,它设计得相当简单,但同时又内涵丰富,应用广泛。介绍了一种应用Sieve语言的电子邮件过滤系统。     

双足机器人实时障碍检测视觉系统

提出一种双足步行机器人的实时障碍检测视觉系统．基于图像平面与机器人行走地面之间的映射变换矩阵的唯一性准则，判别图像中的像点是否位于地面上，高于或低于地面的点被认为是障碍点，为减少实际行走过程中系统外部和内部参数变化对映射变换矩阵的影响，系统加入了在线校正映射变换矩阵模块．在提取出障碍物体边缘后，通过对其三维信息的简单恢复，建立了机器人行走空间的障碍投影图．该系统计算量小，可靠性强，能基本满足双足步行机器人实时避障的要求。     

Set-oriented data mining in relational databases

Data mining is an important real-life application for businesses. It is critical to find efficient ways of mining large data sets. In order to benefit from the experience with relational databases, a set-oriented approach to mining data is needed. In such an approach, the data mining operations are expressed in terms of relational or set-oriented operations. Query optimization technology can then be used for efficient processing.

In this paper, we describe set-oriented algorithms for mining association rules. Such algorithms imply performing multiple joins and thus may appear to be inherently less efficient than special-purpose algorithms. We develop new algorithms that can be expressed as SQL queries, and discuss optimization of these algorithms. After analytical evaluation, an algorithm named SETM emerges as the algorithm of choice. Algorithm SETM uses only simple database primitives, viz., sorting and merge-scan join. Algorithm SETM is simple, fast, and stable over the range of parameter values. It is easily parallelized and we suggest several additional optimizations. The set-oriented nature of Algorithm SETM makes it possible to develop extensions easily and its performance makes it feasible to build interactive data mining tools for large databases.     

A functional approach to database updates

PFL is a functional database language in which functions are defined equationally and bulk data is stored using a special class of functions called selectors. It is a lazy language, supports higher-order functions, has a strong polymorphic type inference system, and allows new user-defined data types and values to be declared. All functions, types and values persist in a database. Functions can be written which update all aspects of the database: by adding data to selectors, by defining new equations, and by introducing new data types and values. PFL is “semi-referentially transparent”, in the sense that whilst updates are referentially opaque and are executed destructively, all evaluation is referentially transparent. Similarly, type checking is “semi-static” in the sense that whilst updates are dynamically type checked at run time, expressions are type checked before they are evaluated and no type errors can occur during their evaluation.

In this paper we examine the expressiveness of PFL with respect to updates, and illustrate the language by developing a number of general purpose update functions, including functions for restructuring selectors, for memoisation, and for generating unique system identifiers. We also provide a translation mechanism between Datalog programs and equations, and show how different Datalog evaluation strategies can be supported.     

基于谓词及句义类型块的汉语句义类型识别

从现代汉语语义学角度,可将句义类型划分为简单句义、复杂句义、复合句义和多重句义4种。作为在整体上对句义结构进行描述的方式之一,句义类型识别是对汉语句子进行完整句义结构分析的重要步骤。该文基于谓词及句义类型块提出了一种汉语句义类型识别的方法,实现了4种句义类型的识别。该方法先通过句中谓词的个数进行初步识别判断出部分简单句,再对剩余的句子先用C4.5机器学习的方法得到句中谓词经过的最大句义类型块的个数,再结合句法结构中顶端句子节点进行判决,最终给出剩余句子的句义类型判定结果。实验采用BFS-CTC汉语标注语料库中10221个句子进行开集测试,句义类型的整体识别准确率达到97.6%,为基于现代汉语语义学的研究奠定了一定的技术研究基础。     

Relaxing the homogeneity assumption in usability testing

Much attention has been paid to the question of how many subjects are needed in usability research. Virzi (1992) modelled the accumulation of usability problems with increasing numbers of subjects and claimed that five subjects are sufficient to find most problems. The current paper argues that this answer is based on an important assumption, namely that all types of users have the same probability of encountering all usability problems. If this homogeneity assumption is violated, then more subjects are needed. A modified version of Virzi's model demonstrates that the number of subjects required increases with the number of heterogeneous groups. The model also shows that the more distinctive the groups, the more subjects will be required. This paper will argue that the simple answer 'five' cannot be applied in all circumstances. It most readily applies when the probability that a user will encounter a problem is both high and similar for all users. It also only applies to simple usability tests that seek to detect the presence, but not the statistical prevalence, of usability problems.     

Comparing data type specifications via their normal forms

A simple technique is presented for verifying that two abstract data type specifications are equivalent in that they have isomorphic initial algebras. The method uses normal forms to attempt reducing the number of equations to be checked. It is applied to a simple example and some extensions, and related problems are also discussed.     

Efficient handling of tuples with embedded large objects

Modern database systems and storage manager toolkits usually provide a large object abstraction. Very often large objects are not used as standalone entities, but rather embedded within an aggregate of different types, i.e. a tuple. Depending on the large object's size and access probability, query performance is determined by the representation of the large object: either inlined within the aggregate or swapped out to a separate object. This paper describes a sound and general large object interface extension which automatically switches the representation of large objects according to their actual size. The optimum threshold size for switching the large object's representation is determined, based upon a linear cost model. Furthermore, a SHORE-based implementation and its performance are presented. It turns out that switching the representation of large objects yields great performance improvements for objects whose size is varying from quite small to large.     

一种带约束的多态类型系统

本文讨论了一种带约束的多态类型系统,引入了约束类型,约束与全称量化的结合使得参数化多态函数的应用更安全,同时也为重工的表示和实现提供了一个新的途径,提高了类型表示的抽象度。本文讨论的类型系统具有两个不同层次的类型结构,约束的引入与肖去是不同层次上的操作,最后,本文人出了类型检查算法Ｗｒ,并证明了此算法中约束的可满足性是可判定的。     

基于类型系统的元数据模型

本研究了程序设计语言的类型系统与数据模型的；认识到类型间关系是表示数据模型的一种。基地这一思想，提出了ＰＣＴ类型描述语言及其基于ＰＣＴ的元数据模型，以描述多种数据模型，ＰＣＴ将Ｃ＋＋类型系统与一阶谓词演算相结合，可以形式化描述特写数据模型所规定的多方面规范。     

State space measures of robustness of pole locations for structured and unstructured perturbations

Measures of pole location robustness for linear feedback systems are derived from a state space model of the system. The robustness tests ensure that the eigenvalues of the perturbed systems matrix A + E remain in a desired region D of the complex plane containing the eigenvalues of the nominal system matrix A. The region D may be any open set of the complex plane whatsoever. The results are expressed in terms of induced matrix norms and apply to structured perturbations of the form E = BΔC, where B and C define the structure of E, and may be nonsquare matrices. Rank one perturbations E of minimal norm and with the given structure that will cause A + E to have an eigenvalue outside of D are constructed for the cases when the matrix norm is induced by the vector 1-norm or the vector ∞-norm. The advantages of having robustness measures for several matrix norms that can be computed are illustrated with a simple example that demonstrates how the conservatism of single tests can be reduced using several tests (i.e. several matrix norms). A method for computing numerically the robustness measures for particular norms is presented. It can be used to compute, with a guaranteed degree of accuracy, the maximum of the norm of the frequency response of a system.     

Encoding of Multiple Inheritance Hierarchies and Partial Orders

Efficient implementation of type inclusion is an important feature of object oriented programming languages with multiple inheritance. The idea is to associate to each type a subset of a set S ={1,..., k } such that type inclusion coincides with subset inclusion. Such an embedding of types into 2 ^S (the lattice of all subsets of S ) is called a bit‐vector encoding of the type hierarchy. In this paper, we show that most known bit‐vector encoding methods can be inserted on a general theoretical framework using graph coloration, namely the notion of a simple encoding . We use the word simple because all these methods are heuristics for the general bit‐vector encoding problem, known as the 2‐dimension problem. First we provide a correct algorithm for partial orders based on simple encoding, improving the algorithm of Krall, Vitek, and Horspool (1997). Second we show that finding an optimal simple encoding is an NP‐hard problem. We end with a discussion on some practical issues.     

A new routing algorithm for multirate rearrangeable Clos networks

In this paper, we study the problem of finding routing algorithms on the multirate rearrangeable Clos networks which use as few number of middle-stage switches as possible. We propose a new routing algorithm called the “grouping algorithm”. This is a simple algorithm which uses fewer middle-stage switches than all known strategies, given that the number of input-stage switches and output-stage switches are relatively small compared to the size of input and output switches. In particular, the grouping algorithm implies that m = 2n+(n−1)/2^k is a sufficient number of middle-stage switches for the symmetric three-stage Clos network C(n,m,r) to be multirate rearrangeable, where k is any positive integer and rn/(2^k−1).     

Distributed selectsort sorting algorithms on broadcast communication networks

In this paper, a distributed selectsort algorithm and a parameterized selectsort algorithm are presented to be applied on distributed systems for cases when N P where N is the number of elements to be sorted and P is the number of processors in the system. The distributed system considered in this paper uses a broadcasting channel for communication between processors. We show that the number of messages required for the parameterized selectsort algorithm is independent of N and is of complexity O(P), which is optimal in a distributed system with P processors. Furthermore, the amount of communication required in terms of elements is N + O(P³) and the computation time complexity is O((N/P)lgN + P²lg(N/P)). Hence, when N P³, the computation time complexity is O((N/P)lgN), which is optimal using P processors. In addition, this parameterized algorithm provides us with a parameter K such that by choosing the value of K allows us to trade among processing requirement, memory requirement, and communication requirement. It is shown that this parameterized algorithm can reduce the communication requirements significantly while only slightly increasing the computation requirements.