Context-aware Retrieval: Exploring a New Environment for Information Retrieval and Information Filtering

The opportunities for context-aware computing are fast expanding. Computing systems can be made aware of their environment by monitoring attributes such as their current location, the current time, the weather, or nearby equipment and users. Context-aware computing often involves retrieval of information: it introduces a new aspect to technologies for information delivery; currently these technologies are based mainly on contemporary approaches to information retrieval and information filtering. In this paper, we consider how the closely related, but distinct, topics of information retrieval and information filtering relate to context-aware retrieval. Our thesis is that context-aware retrieval is as yet a sparsely researched and sparsely understood area, and we aim in this paper to make a start towards remedying this.     

When are Personal Technologies for Children?

This paper will discuss the various issues surrounding personal technologies for children. Three critical questions will be discussed: Why can technology be important for children? What activities can technology support? And what changes should be considered for the future?     

Optimality-criteria-based probabilistic structural design

The possibility of extending absolute minimum weight designs for sandwich beam systems or fibre-reinforced beams and plates is considered when both the extreme loading applied to the system and the beam bending resistance properties are described in probabilistic rather than deterministic terms. It is shown that such an extension is possible provided certain plausible assumptions are made about the probabilistic modelling of the system. Examples considered include simple and continuous beams under loading of uncertain magnitude, direction or location. It is shown that the classical (deterministic) optimal solutions remain valid under reasonable assumptions. The extension of the probabilistic solutions to a wider class of examples is discussed. Received October 20, 2000     

Solving Third Order Differential Equations with Maximal Symmetry Group

The largest group of Lie symmetries that a third-order ordinary differential equation (ode) may allow has seven parameters. Equations sharing this property belong to a single equivalence class with a canonical representative v ^′′′(u)=0. Due to this simple canonical form, any equation belonging to this equivalence class may be identified in terms of certain constraints for its coefficients. Furthermore a set of equations for the transformation functions to canonical form may be set up for which large classes of solutions may be determined algorithmically. Based on these steps a solution algorithm is described for any equation with this symmetry type which resembles a similar scheme for second order equations with projective symmetry group. Received March 9, 2000; revised June 8, 2000     

On Constructing Unit Triangular Matrices with Prescribed Singular Values

We propose an efficient algorithm for computing a unit lower triangular n×n matrix with prescribed singular values of O(n ²) cost. This is a solution of the question raised by N. J. Higham in [4, Problem 26.3, p. 528]. Received July 21, 1999; revised November 4, 1999     

A Cascadic Multigrid Algorithm for Semilinear Indefinite Elliptic Problems

We propose a cascadic multigrid algorithm for a semilinear indefinite elliptic problem. We use a standard finite element discretization with piecewise linear finite elements. The arising nonlinear equations are solved by a cascadic organization of Newton's method with frozen derivative on a sequence of nested grids. This gives a simple version of a multigrid method without projections on coarser grids. The cascadic multigrid algorithm starts on a comparatively coarse grid where the number of unknowns is small enough to obtain an approximate solution within sufficiently high precision without substantial computational effort. On each finer grid we perform exactly one Newton step taking the approximate solution from the coarsest grid as initial guess. The linear Newton systems are solved iteratively by a Jacobi-type iteration with special parameters using the approximate solution from the previous grid as initial guess. We prove that for a sufficiently fine initial grid and for a sufficiently good start approximation the algorithm yields an approximate solution within the discretization error on the finest grid and that the method has multigrid complexity with logarithmic multiplier. Received February 1999, revised July 13, 1999     

A Class of Smoothers for Saddle Point Problems

In this paper smoothing properties are shown for a class of iterative methods for saddle point problems with smoothing rates of the order 1/m, where m is the number of smoothing steps. This generalizes recent results by Braess and Sarazin, who could prove this rates for methods where, in the context of the Stokes problem, the pressure correction equation is solved exactly, which is not needed here. Received December 4, 1998; revised April 14, 2000     

基于内容的网页特征提取

文章主要研究基于内容的中文网页的特征提取技术,具体介绍了分词词典的建造方法,网页正文、标记信息和超链信息的特征提取。通过对旅游类网页的实验结果显示,文中的方法和应用效果良好。     

实现安全数据库的一种方法——数据库安全通信服务

提出了实现安全数据库的一种方法———数据库安全通信服务,它通过使用(1)不同种类和不同算法强度的密钥算法;(2)密钥的适时更新;(3)加密后的数据包与本地机器环境和客户端的当前用户相关;(4)数据包的还原校验与本地机器环境和客户端的当前用户相关;(5)基于X.509证书的身份识别和访问控制策略,等方法和技术极大地提高了数据库及其通信系统的安全性,具有较高的实用价值。     

A graph-theoretic model for optimizing queries involving methods

Traditional algorithms for optimizing the execution order of joins are no more valid when selections and projections involve methods and become very expensive operations. Selections and projections could be even more costly than joins such that they are pulled above joins, rather than pushed down in a query tree. In this paper, we take a fundamental look at how to approach query optimization from a top-down design perspective, rather than trying to force one model to fit into another. We present a graph model which is designed to characterize execution plans. Each edge and each vertex of the graph is assigned a weight to model execution plans. We also design algorithms that use these weights to optimize the execution order of operations. A cost model of these algorithms is developed. Experiments are conducted on the basis of this cost model. The results show that our algorithms are superior to similar work proposed in the literature. Received 20 April 1999 / Accepted 9 August 2000 Published online 20 April 2001