Term-graph Rewriting in Tom Using Relative Positions

In this paper, we present the implementation in Tom of a de Bruijn indices generalization allowing the representation of term-graphs over an algebraic signature. By adding pattern matching and traversal controls to Java, Tom is a well-suited environment for defining program transformations or analyses. As some analyses, e.g. based on control flow, require graph-like structures, the use of this formalism is a natural way of expressing them by graph rewriting.     

From Chemical Rules to Term Rewriting

In this paper, rule-based programming is explored in the field of automated generation of chemical reaction mechanisms. We explore a class of graphs and a graph rewriting relation where vertices are preserved and only edges are changed. We show how to represent cyclic labeled graphs by decorated labeled trees or forests, then how to transform trees into terms. A graph rewriting relation is defined, then simulated by a tree rewriting relation, which can be in turn simulated by a rewriting relation on equivalence classes of terms. As a consequence, this kind of graph rewriting can be implemented using term rewriting. This study is motivated by the design of the GasEl system for the generation of kinetics reactions mechanisms. In GasEl, chemical reactions correspond to graph rewrite rules and are implemented by conditional rewriting rules in ELAN. The control of their application is done through the ELAN strategy language.     

Formal Proofs About Rewriting Using ACL2

We present an application of the ACL2 theorem prover to reason about rewrite systems theory. We describe the formalization and representation aspects of our work using the first-order, quantifier-free logic of ACL2 and we sketch some of the main points of the proof effort. First, we present a formalization of abstract reduction systems and then we show how this abstraction can be instantiated to establish results about term rewriting. The main theorems we mechanically proved are Newman's lemma (for abstract reductions) and Knuth–Bendix critical pair theorem (for term rewriting).     

从多地址空间到单地址空间再到无地址空间

在分析单地址空间操作系统的优点及其所存在问题的基础上,提出了无地址空间操作系统的思想,并介绍了一个无地址空间操作系统原型.在无地址空间操作系统中,没有进程虚拟空间的概念,指令直接对文件寻址,进程直接在文件上运行.与单地址空间操作系统相比,无地址空间操作系统不仅具有单地址空间操作系统的优点,而且能够避免单地址空间操作系统中存在的不足.     

Rewriting Union Queries Using Views

The problem of finding contained rewritings of queries using views is of great importance in mediated data integration systems. In this paper, we first present a general approach for finding contained rewritings of unions of conjunctive queries with arbitrary built-in predicates. Our approach is based on an improved method for testing conjunctive query containment in this context. Although conceptually simple, our approach generalizes previous methods for finding contained rewritings of conjunctive queries and is more powerful in the sense that many rewritings that can not be found using existing methods can be found by our approach. Furthermore, implication constraints (Zhang, X., & Ozsoyoglu, Z.M. (1997). Implication and referential constraints: A new formal resaoning. IEEE TKDE, 9(6):894–910, Now/Dec.) over the base relations can be easily handled. We then present a simplified approach which is less complete, but is much faster than the general approach, and it still finds maximum rewritings in several special cases. Our general approach finds more rewritings than previous algorithms such as the Bucket and the resolution-based algorithms. Our simplified approach generalizes the U-join and the MiniCon algorithms with no loss of efficiency.     

Mechanizing Weakly Ground Termination Proving of Term Rewriting Systems by Structural and Cover-Set Inductions

The paper presents three formal proving methods for generalized weakly ground terminating property, i.e., weakly terminating property in a restricted domain of a term rewriting system, one with structural induction, one with cover-set induction, and the third without induction, and describes their mechanization based on a meta-computation model for term rewriting systems-dynamic term rewriting calculus. The methods can be applied to non-terminating, non-confluent and/or non-left-linear term rewriting systems. They can do "forward proving" by applying propositions in the proof, as well as "backward proving" by discovering lemmas during the proof.     

From Functional Programs to Interaction Nets via the Rewriting Calculus

We use the ρ-calculus as an intermediate language to compile functional languages with pattern-matching features, and give an interaction net encoding of the ρ-terms arising from the compilation. This encoding gives rise to new strategies of evaluation, where pattern-matching and 'traditional' β-reduction can proceed in parallel without overheads.     

Independence of Containing Patterns Property and Its Application in Tree Pattern Query Rewriting Using Views

We show that several classes of tree patterns observe the independence of containing patterns property, that is, if a pattern is contained in the union of several patterns, then it is contained in one of them. We apply this property to two related problems on tree pattern rewriting using views. First, given view V and query Q, is it possible for Q to have an equivalent rewriting using V which is the union of two or more tree patterns, but not an equivalent rewriting which is a single pattern? This problem is of both theoretical and practical importance because, if the answer is no, then, to find an equivalent rewriting of a tree pattern using a view, we should use more efficient methods, such as the polynomial time algorithm of Xu and Özsoyoglu (2005), rather than try to find the union of all contained rewritings (which takes exponential time in the worst case) and test its equivalence to Q. Second, given a set S of views, we want to know under what conditions a subset S′ of S is redundant in the sense that for any query Q, the contained rewritings of Q using the views in S′ are contained in those using the views in S???S′. Solving this problem can help us to, for example, choose the minimum number of views to be cached, or better design the virtual schema in a mediated data integration system, or avoid repeated calculation in query optimization. For the first problem, we identify several classes of tree patterns for which the equivalent rewriting can be expressed as a single tree pattern. For the second problem, we present necessary and sufficient conditions for S′ to be redundant with respect to some classes of tree patterns. For both problems we consider extension to cases where there are rewritings using the intersection of multiple views and/or where a schema graph is present.     

Logical Approach to Capability-Based Rewriting in a Mediator for WebSources

A logic-based specification for Capability-Based Rewriting (CBR) in web query processing is presented. Within this approach it is shown how Semantic Query Optimization (SQO) can be used to improve the performance of a web query optimizer. Our approach allows for the characterization of different CBR tools and their properties in a uniform and generic manner. It also reveals important optimization opportunities (based on SQO) which are commonly ignored in existing CBR tools.     

Java程序内存低效使用问题的分析

Java程序内存的低效使用是导致其性能问题的主要因素。该文分析了泄漏对象、蚍蜉对象和空闲对象3类导致内存低效使用的情况,探讨解决上述问题的方法,并提出构造对象行为模式。实验结果表明,该方案是有效的。     

基于Linux内核的动态内存管理机制的实现

在软件开发过程中,共享内存经常会遇到一个进程消耗太多内存导致其他进程无法得到需要内存的潜在问题,针对该问题,基于Linux内核实现一种动态内存管理机制,该机制能够限制每个进程所能申请的最大内存数,同时可以避免进程内存泄露造成的系统崩溃。实验结果表明,该机制效率高、且易用性好。     

基于Linux内核的动态内存管理机制的实现

在软件开发过程中,共享内存经常会遇到一个进程消耗太多内存导致其他进程无法得到需要内存的潜在问题,针对该问题,基于Linux内核实现一种动态内存管理机制,该机制能够限制每个进程所能申请的最大内存数,同时可以避免进程内存泄露造成的系统崩溃。实验结果表明,该机制效率高、且易用性好。     

Using FORAY Models to Enable MPSoC Memory Optimizations

With the technology advances it becomes feasible to implement a large multiprocessor system on a single chip. In such Systems-on-Chip (SoCs), a significant portion of energy is spent in the memory subsystem. There are several approaches reducing this energy, including the ones at physical, architecture and algorithmic levels. Classical approaches, including algorithmic and some architectural approaches, use static analysis and transformation of the application source code. However, often it is not possible to perform static analysis and optimization of a program’s memory access behavior unless the program is written in an easily analyzable form, e.g., free from pointer arithmetic. In this paper, we introduce the FORAY model of a program that allows aggressive analysis of the application’s memory behavior and enables such optimizations on arbitrary code which are not possible to apply otherwise. We then present FORAY-GEN: an automated profile-based approach for extraction of the FORAY model from the original program. We also outline our approach in applying FORAY-GEN for multiprocessor SoCs. We demonstrate how FORAY-GEN enhances applicability of other memory subsystem optimization approaches, resulting in an average of two times increase in the number of memory references that can be analyzed by existing static approaches.     

容易记忆的地铁站空间

在地下空间,特别是在比较复杂的综合性地下空间中,人们不易定位定向。目前在上海地铁空间环境设计不够成熟,可以作为很好的研究素材。上海地铁这样站台风格差异不大的地铁空间里,使用者仍然会不断寻求可记忆的点来加强对空间的熟悉程度。了解这些记忆点是什么,能帮助我们在设计中更好的发挥其作用,使得地铁空间容易被记忆,变得更加人性化。     

空间分析技术在数字城管系统中的应用

空间分析在GIS中扮演着越来越重要的角色。该文以厦门市数字城市信息管理系统为研究对象,该系统在大屏幕监督指挥子系统中运用了GIS技术．同时基于GIS实际需求使用了改进的空间分析算法以便实现系统功能。改进的空间算法以传统空间分析算法为基础．针对空间数据量庞大检索缓慢的问题,提出了一种基于方向性的最短路径搜索方法。     

解析Symbian操作系统内存管理机制

Symbian操作系统中,使用TRAP机制捕获系统异常,控制内存分配过程。清除栈结构可以保证当发生异常产生的情况下,系统不会出现内存泄露。对自定义类型的两段构造方法,可以修改C＋＋默认的构造规则,保证内存安全。     

运行时存储管理探讨

为了在软件工程实践中有效利用运行时存储的空间,对动态堆内存管理的两种技术显式堆管理和自动堆管理分别进行了深入的讨论,分析了这两种技术各自的优点和缺陷,并根据笔者的实践经验,提出了一些解决缺陷的方法。     

浅析室内商业空间中的尺度

本文通过对室内商业空间中尺度的形成原因、影响因素的分析,尝试性地提出了室内商业空间中的尺度三个层级:主要包含空间的尺度层级(界面),结构、构件的尺度层级,陈设、设施的尺度层级。对于室内商业空间中尺度问题的把握,不仅是对消费者生理需求的尊重,更是满足心理需求的体现。     

非线性状态空间模型遗忘性研究

动态系统的遗忘性是描述系统行为主要取决于其近期输入的概念，与系统的稳定性、鲁棒性等密切相关。对于非线性状态空间模型，遗忘性在很弱的条件下与整体一致非常吸引等价。系统在凸集或不变区集上的遗忘性可由一类特殊Ｌｙａｐｕｎｏｖ函数的存在性保证。遗忘区域的大小可利用矩阵不等式来估计。