Context-Free Series on Trees

We investigate context-free (CF) series on trees with coefficients on a semiring; they are obtained as components of the least solutions of systems of equations having polynomials on their right-hand sides. The relationship between CF series on trees and CF tree-grammars and recursive program schemes is also examined. Polypodes, a new algebraic structure, are introduced in order to study in common series on trees and words and applications are given.     

Active Context-Free Games

An Active Context-Free Game is a game with two players (ROMEO and JULIET) on strings over a finite alphabet. In each move, JULIET selects a position of the current word and ROMEO rewrites the corresponding letter according to a rule of a context-free grammar. JULIET wins if a string of the regular target language is reached. The complexity of deciding the existence of winning strategies for JULIET is investigated, depending on properties of the grammar and of the target language, and on restrictions on the strategy.     

Spinal-Formed Context-Free Tree Grammars

In this paper we introduce a restricted model of context-free tree grammars called spine grammars, and study their formal properties including considerably simple normal forms. Recent research on natural languages has suggested that formalisms for natural languages need to generate a slightly larger class of languages than context-free grammars, and for that reason tree adjoining grammars have been widely studied relating them to natural languages. It is shown that the class of string languages generated by spine grammars coincides with that of tree adjoining grammars. We also introduce acceptors called linear pushdown tree automata, and show that linear pushdown tree automata accept exactly the class of tree languages generated by spine grammars. Linear pushdown tree automata are obtained from pushdown tree automata with a restriction on duplicability for the pushdown stacks. Received May 29, 1998, and in revised form April 27, 1999, and in final form May 10, 1999.     

Tutorial Series 4 Perspectives on Personal Computing

Products of a technology-fueled revolution to put computing in the hands of many people, personal computers are quickly becoming tools as essential as the telephone.     

Context-Free Event Domains Are Recognizable

The possibly non-distributive event domains which arise from Winskel's event structures with binary conflict are known to coincide with the domains of configurations of Stark's trace automata. We prove that whenever the transitive reduction of the order on finite elements in an event domain is a context-free graph in the sense of Müller and Schupp, the event domain may also be generated from a finite trace automaton, where both the set of states and the concurrent alphabet are finite. We show that the set of graph grammars which generate event domains is a recursive set. We obtain altogether an effective procedure which decides from an unlabeled graph grammar whether it generates an event domain and which constructs in that case a finite trace automaton recognizing that event domain.     

Inferring Context-Free Grammars for Domain-Specific Languages

In the area of programming languages, context-free grammars (CFGs) are of special importance since almost all programming languages employ CFG's in their design. Recent approaches to CFG induction are not able to infer context-free grammars for general-purpose programming languages. In this paper it is shown that syntax of a small domain-specific language can be inferred from positive and negative programs provided by domain experts. In our work we are using the genetic programming approach in grammatical inference. Grammar-specific heuristic operators and nonrandom construction of the initial population are proposed to achieve this task. Suitability of the approach is shown by examples where underlying context-free grammars are successfully inferred.     

基于上下文无关文法的可逆变换模型

可逆变换和双向变换等数据转换问题一直是近年来的研究热点,研究人员针对该问题提出了大量相关的语言和模型。但是,这些实现往往建立在一种新的计算模型上,从而导致需要花费较大的学习成本去了解计算模型。另一方面,作为语法解析的基本工具,上下文无关文法对于绝大多数程序员来说都是不陌生的。提出了一种基于上下文无关文法的计算模型,用来构造字符串上的可逆变换,并对其性质和表达能力进行了探讨。采用Scheme语言实现了该计算模型,并通过在MIPS指令集上进行汇编和反汇编开发验证了该模型。验证结果表明,该模型具有较强的表达能力,在添加小型的公共数值变换模块后,可以完整地实现MIPS指令集上的汇编和反汇编。     

Decidability of Branching Bisimulation on Normed Commutative Context-Free Processes

We investigate normed commutative context-free processes (Basic Parallel Processes). We show that branching bisimilarity admits the bounded response property: in the Bisimulation Game, Duplicator always has a response leading to a process of size linearly bounded with respect to the Spoiler’s process. The linear bound is effective, which leads to decidability of branching bisimilarity. For weak bisimilarity, we are able merely to show existence of some linear bound, which is not sufficient for decidability. We conjecture however that the same effective bound holds for weak bisimilarity as well. We suppose that further elaboration of novel techniques developed in this paper may be sufficient to demonstrate decidability.     

Latent Variable Model for Estimation of Distribution Algorithm Based on a Probabilistic Context-Free Grammar

Estimation of distribution algorithms are evolutionary algorithms using probabilistic techniques instead of traditional genetic operators. Recently, the application of probabilistic techniques to program and function evolution has received increasing attention, and this approach promises to provide a strong alternative to the traditional genetic programming techniques. Although a probabilistic context-free grammar (PCFG) is a widely used model for probabilistic program evolution, a conventional PCFG is not suitable for estimating interactions among nodes because of the context freedom assumption. In this paper, we have proposed a new evolutionary algorithm named programming with annotated grammar estimation based on a PCFG with latent annotations, which allows this context freedom assumption to be weakened. By applying the proposed algorithm to several computational problems, it is demonstrated that our approach is markedly more effective at estimating building blocks than prior approaches.      

移动计算中基于Rough Set的时间序列研究与应用

提出了基于Rough Set在移动计算环境中进行数据挖掘的系统模型,给出了进行数据挖掘的具体算法,介绍了由实时时态信息系统转换为时态信息系统的平均时间间隔方法,以及由时态信息系统转换为传统信息系统的增量分析方法,最后给出了实例和应用结果.     

Structural Properties of Context-Free Sets of Graphs Generated by Vertex Replacement

We establish that a Vertex Replacement set of graphs, i.e., a set of graphs generated by a C-edNCE or, equivalently, by a separated handle rewriting graph grammar is Hyperedge Replacement, i.e., is generated by a hyperedge replacement graph grammar, iff its graphs do not contain arbitrary large complete bipartite graphs K_{n, n} as subgraphs. Another equivalent condition is that its graphs have a number of edges that is linearly bounded in terms of the number of vertices. These properties are decidable by means of an appropriate extension of the theorem by Parikh that characterizes the commutative images of context-free languages. We extend these results to hypergraphs.     

一种上下文无关语言语法树的存储模式及其应用

针对上下文无关语言的句子所对应的语法树G树的表示形式提出了一种关系数据库的存储形式.这种存储形式的优点是：表示形式一致;句子分析简单;语句执行速度快.这种存储形式作为一种上下文无关语言的中间语言的形式可以直接交付解释器（抽象机）执行.同时介绍基于这种表示形式的上下文无关句子的编辑器.编辑器是基于Web的交互式语法制导生成方式实现的.这种表示与存储形式被用于一种描述过程性知识的函数式语言.     

The Failure of the Strong Pumping Lemma for Multiple Context-Free Languages

Seki et al. (Theor. Comput. Sci. 88(2):191–229, 1991) showed that every m-multiple context-free language L is weakly 2m-iterative in the sense that either L is finite or L contains a subset of the form \(\{ u_{0} w_{1}^{i} u_{1} \cdots w_{2m}^{i} u_{2m} \mid i \in \mathbb {N}\}\) , where w ₁?w _2n ≠ε. Whether every m-multiple context-free language L is 2m-iterative, that is to say, whether all but finitely many elements z of L can be written as z=u ₀ w ₁ u ₁?w _2m u _2m with w ₁?w _2m ≠ε and \(\{ u_{0} w_{1}^{i} u_{1} \cdots w_{2m}^{i} u_{2m} \mid i \in \mathbb {N}\} \subseteq L\) , has been open. We show that there is a 3-multiple context-free language that is not k-iterative for any k.     

Integrated Risk Analysis for a Commercial Computing Service in Utility Computing

Recent technological advances in Grid computing enable the virtualization and dynamic delivery of computing services on demand to realize utility computing. In utility computing, computing services will always be available to the users whenever the need arises, similar to the availability of real-world utilities, such as electrical power, gas, and water. With this new outsourcing service model, users are able to define their service needs through Service Level Agreements (SLAs) and only have to pay when they use the services. They do not have to invest on or maintain computing infrastructures themselves and are not constrained to specific computing service providers. Thus, a commercial computing service will face two new challenges: (i) what are the objectives or goals it needs to achieve in order to support the utility computing model, and (ii) how to evaluate whether these objectives are achieved or not. To address these two new challenges, this paper first identifies four essential objectives that are required to support the utility computing model: (i) manage wait time for SLA acceptance, (ii) meet SLA requests, (iii) ensure reliability of accepted SLA, and (iv) attain profitability. It then describes two evaluation methods that are simple and intuitive: (i) separate and (ii) integrated risk analysis to analyze the effectiveness of resource management policies in achieving the objectives. Evaluation results based on simulation successfully demonstrate the applicability of separate and integrated risk analysis to assess policies in terms of the objectives. These evaluation results which constitute an a posteriori risk analysis of policies can later be used to generate an a priori risk analysis of policies by identifying possible risks for future utility computing situations.     

On the Expressive Power of Abstract Categorial Grammars: Representing Context-Free Formalisms

We show how to encode context-free string grammars, linear context-free tree grammars, and linear context-free rewriting systems as Abstract Categorial Grammars. These three encodings share the same constructs, the only difference being the interpretation of the composition of the production rules. It is interpreted as a first-order operation in the case of context-free string grammars, as a second-order operation in the case of linear context-free tree grammars, and as a third-order operation in the case of linear context-free rewriting systems. This suggest the possibility of defining an Abstract Categorial Hierarchy.