MAS中基于Ontology的知识表示与推理研究

采用基于Ontology的知识表示方法,解决多Agent的知识表示和共享问题,实现知识的自动推理和获取,实现多Agent之间语义理解,体现Agent的智能特征.在多Agent原型旅游系统中,采用OWL描述Ontology定义相关领域的知识表示与推理,为Agent之间的学习、协商,进一步交互通信打下基础.     

基于自然语言理解的专家系统研究

在论述了面向自然语言文本的知识供应方法已有研究之后,提出了面向推理设计语义关系标记,将自然语言理解与推理技术相结合,使自然语言理解结果可转化为便于计算机推理的语句。立足科技文献开发语义关系树库,提出面向语义关系分析的语句相似度计算方法,实现基于统计与规则相结合的自然语言语义关系分析,使自然语言科技文献可成为专家系统知识库,解决专家系统知识库表现形式不统一及知识获取的瓶颈。     

背景知识在自动分词和篇章理解中的应用

自然语言理解可以分为五个层次；单词、短评、句子、段落和篇章，每层次都与其它层次相关联，背景知识包含了所有层次的语言元素及其在实际环境中的使用，本文着重讨论了背景知识在汉语自动分词和基于语义关联的篇章理解。     

基于Ontology的信息查询系统模型研究

当前,网络信息资源呈现爆炸式增长趋势,用户对信息查询的要求也越来越高,传统的各种信息查询技术已经很难满足这种要求。未来的因特网作为人类的信息库、知识库,应该支持用户以自然语言的方式来完成信息查询,并具备理解语义,进行自动扩展、联想的智能化查询系统。该文提出一个基于Ontology的信息查询系统模型,实现支持自然语言的理解和语义层面的智能化查询功能。     

语义Web中工程设计类知识表示研究

研究了如何在语义Web中，实现工程设计类知识的表示与应用。对工程设计类各种异构知识进行统一描述，在此基础上，运用RDF(S)技术，建立了语义Web环境下，工程设计类知识的Ontology。提出了基于语义Web的知识存储模型以及面向上层应用程序的接口设计，为语义Web环境下工程设计类知识管理系统的开发提供了底层平台。     

面向水利信息资源的智能问答系统构建与应用

当前特定领域的问答系统主要采用基于关键字匹配的方法完成问答,类似水库大坝的建成时间、坝高等,无法充分理解用户自然语言提问的检索意图并给出准确回答。为此基于知识图谱技术,利用语义解析方法,本文设计并开发面向水利信息资源的智能问答系统。针对语义解析自然语言问句转化为结构化查询语句需要多步操作,容易导致语义鸿沟问题,还为了后续基于知识表示的问答方法,积累用户语料,本文提出一种语料扩展方法构建语料库。     

基于知识树的领域知识组织和应用*

在分析已有知识表示方法优缺点的基础上,提出一种高效的知识表达模型——概念知识树。概念知识树模型不仅结构性好、表达能力强,而且在应用中具有良好的适应性和延展性,现主要应用于信息检索和自然语言理解领域。以旅游领域为背景,用概念知识树作为表达模型建立相应的领域知识体系,并在此基础之上实现了一个旅游智能分析系统。该系统可在对用户需求(自然语言)进行一定程度语义理解的基础上,根据所建立的知识体系自动进行语义匹配,最终返回满足用户需要以及相关的旅游路线信息。     

基于概念层次网络的知识表示与本体建模

知识表示是自然语言理解的重要基础。知识表示不统一、语义信息无法系统化利用是目前存在的亟待解决的问题。要解决这个问题,就要解决语义知识表示的问题。该文基于概念层次网络,描述了词语、句子和篇章层面的语义知识表示方法。基于文中描述的词汇层面的表示方法,构建了一个多语言本体知识库。该知识库的知识表示方法不仅可以为知识表示理论研究提供基础,还可以为自然语言处理相关领域的应用提供资源支持。     

汉语语义选择限制知识的自动获取研究

语义选择限制刻画了谓语对论元的语义选择倾向,是一种重要的词汇语义知识,对自然语言的句法、语义分析具有重要作用。该文研究汉语语义选择限制知识的自动获取,提出基于HowNet和基于LDA (Latent Dirichlet Allocation)的两种知识获取方法,对方法进行了实验对比与分析。实验表明,前者所获取的知识可理解性更好,后者所获取的知识应用效果更好。两种方法具有很好的互补性,我们提出了一个二者的融合方案。     

面向中文自然语言文档的自动知识抽取方法

自动知识抽取方法可以自动识别并抽取Web文档中与本体匹配的事实知识.利用这些事实知识既可以构建基于知识的服务,也能够为语义Web的实现提供必要的语义数据.但面向自然语言特别是中文自然语言的自动知识抽取非常困难.提出了基于语义Web理论和中文自然语言处理(naturallanguage processing,NLP)技术的自动知识抽取新方法AKE,用聚集体知识概念刻画N元关系知识,能够在不使用大规模语言知识库和同义词表的情况下自动识别中文自然语言文档内容中显式和隐含的简单事实知识和N元关系复杂事实知识.实验结果表明该方法优于目前已知的其他方法.     

From algebraic semantics to denotational semantics for Verilog

This paper considers how the algebraic semantics for Verilog relates with its denotational semantics. Our approach is to derive the denotational semantics from the algebraic semantics. We first present the algebraic laws for Verilog. Every program can be expressed as a guarded choice that can model the execution of a program. In order to investigate the parallel expansion laws, a sequence is introduced, indicating which instantaneous action is due to which exact parallel component. A head normal form is defined for each program by using a locality sequence. We provide a strategy for deriving the denotational semantics based on head normal form. Using this strategy, the denotational semantics for every program can be calculated. Program equivalence can also be explored by using the derived denotational semantics. A short version of this paper appeared in Proc. ICECCS 2006: 11th IEEE International Conference on Engineering of Complex Computer Systems [48]. This work is partially supported by the National Basic Research Program of China (No. 2005CB321904), the National High Technology Research and Development Program of China (No. 2007AA010302) and the National Natural Science Foundation of China (No. 90718004). Jonathan Bowen is a visiting professor at King’s College London and an emeritus professor at London South Bank University.     

Towards a denotational semantics of timed RSL using duration calculus

The Timed RAISE Specification Language(Timed RSL)is an extension of RAISE Specificatioin Language by adding time constructors for specifying real-time applications.Duration Calculus(DC) is a real-time interval logic,which can be used to specify and reason about timing and logical constraints on duration propoerties of Boolean states in a dynamic system.This paper gives a denotational semantics to a subset of Timed RSL expressions,using Duration Calculus extended with super-dense shop modality and notations to capture time point properties of piecewise continuous states of arbitrary types.Using this semantics,the paper pesents a proof rule for verifying Timed RSL iterative expressions and implements the rule to prove the satisfaction by a sample Timed RSL specification of its real-time requrements.     

Interpreting SWRL Rules in RDF Graphs

An unresolved issue in SWRL (the Semantic Web Rule Language) is whether the intended semantics of its RDF representation can be described as an extension of the W3C RDF semantics. In this paper we propose to make the model-theoretic semantics of SWRL compatible with RDF by interpreting SWRL rules in RDF graphs. For dealing with SWRL/RDF rules, we regard ‘Implies’ as an OWL class, and extract all ‘Implies’ rules from an RDF database that represents a SWRL knowledge base. Each ‘Implies’ rule is grounded through mappings built into the semantic conditions of the model theory. Based on the fixpoint semantics, a bottom-up strategy is employed to compute the least Herbrand models.     

On solving efficiently the view selection problem under bag and bag-set semantics

In this paper, we investigate the problem of view selection for workloads of conjunctive queries under bag and bag-set semantics. In particular, for both semantics we aim to limit the search space of candidate viewsets. We also start delineating boundaries between query workloads for which certain even more restricted search spaces suffice. They suffice in the sense that they do not compromise optimality in that they contain at least one of the optimal solutions. We start with the general case for both bag and bag-set semantics, where we give a tight condition that candidate views can satisfy and still the search space (thus limited) does contain at least one optimal solution. We show that these results, for both semantics, reduce the size of the search space significantly. Further on, due to this analysis for both semantics, a delineation of the space of viewsets and the space of the corresponding equivalent rewritings for a certain conjunctive query workload is given. We show that for chain query workloads under both bag and bag-set semantics, taking only chain views may miss optimal solutions, whereas, if we further limit the queries to be path-queries (i.e., chain queries over a single binary relation), then, under bag semantics, path-views suffice. Concentrating to bag-set semantics, we show that the path-viewsets do not suffice for every path-query workload.     

基于参照的对词结构操作语义的归纳学习

心理语言学的研究和认知发展过程证明在语言获得的早期经历了一个自主的归纳学习过程,本文的出发点是语言发展的规律,并将词结构形式语义的获得过程和表示基础放在一个具有统一的语言理解和语言产生机制的语言信息加工模型中来考虑。本文讨论了一个基于实例的机器学习系统,为了获得词结构的形式语义,采用了操作语义的定义,并设计了一个基于参照的发现学习算法,其目的是使语义能伴随例句样本的丰富而精密化。     

Towards proving type safety of .NET CIL

A crucial role in the Microsoft .NET Framework Common Language Runtime (CLR) security model is played by type safety of the Common Intermediate Language (CIL). In this paper, we formally prove type safety of a large subset of CIL. To do so, we begin by specifying the static and dynamic semantics of CIL by providing an abstract interpreter for CIL programs. We then formalize the bytecode verification algorithm, whose job it is to compute a well-typing for a given method. We then prove type safety of well-typed methods, i.e., the execution according to the semantics model of legal and well-typed methods does not lead to any run-time type violations. Finally, to prove CIL’s type safety, we show that the verification algorithm is sound, i.e., the typings it produces are well-typings, and complete, i.e., if a well-typing exists, then the algorithm computes one.     

A structured operational semantics for UML-statecharts

The Unified Modeling Language (UML) has gained wide acceptance in very short time because of its variety of well-known and intuitive graphical notations. However, this comes at the price of an unprecise and incomplete semantics definition. This insufficiency concerns single UML diagram notations on their own as well as their integration. In this paper, we focus on the notation of UML-statecharts. Starting with a precise textual syntax definition, we develop a precise structured operational semantics (SOS) for UML-statecharts. Besides the support of interlevel transitions and in contrast to related work, our semantics definition supports characteristic UML-statechart features like the history mechanism as well as entry and exit actions. Initial submission: 19 February 2002 / Revised submission: 28 October 2002 Published online: 2 December 2002     

Equivalence of formal semantics definition methods

There are numerous methods of formally defining the semantics of computer languages. Each method has been designed to fulfil a different purpose. For example, some have been designed to make reasoning about languages as easy as possible; others have been designed to be accessible to a large audience and some have been designed to ease implementation of languages. Given two semantics definitions of a language written using two separate semantics definition methods, we must be able to show that the two are in fact equivalent. If we cannot do this then we either have an error in one of the semantics definitions, or more seriously we have a problem with the semantics definition methods themselves.Three methods of defining the semantics of computer languages have been considered, i.e. Denotational Semantics, Structural Operational Semantics and Action Semantics. An equivalence between these three is shown for a specific example language by first defining its semantics using each of the three definition methods. The proof of the equivalence is then constructed by selecting pairs of the semantics definitions and showing that they define the same language.A full version of this paper can be accessed via our web page http://www.cs.man.ac.uk/fmethods/ facj.html     

Equivalence of queries that are sensitive to multiplicities

The query equivalence problem has been studied extensively for set-semantics and, more recently, for bag and bag-set semantics. However, SQL queries often combine set, bag and bag-set semantics. For example, an SQL query that returns a multiset of elements may call a subquery or view that returns a set of elements. Queries may access both relations that do not contain duplicates, as well as relations with duplicates. As another example, in SQL one can compute a multiset-union of queries, each of which returns a set of answers. This paper presents combined semantics, which formally models query evaluation combining set, bag and bag-set semantics. The equivalence problem for queries evaluated under combined semantics is studied. A sufficient condition for equivalence is presented. For several important common classes of queries necessary and sufficient conditions for equivalence are presented. An early version of this article appeared in [7]. This paper extends [7] to include bag semantics, in addition to set and bag-set semantics. This work was partially supported by the Israel Science Foundation (Grant 1032/05).