Restricted semantics for default reasoning

In nonmonotonic reasoning there are the problems of inconsistency and incoherence in general, and in default reasoning there may be only one trivial extension or no extension in special. We propose the restricted semantics of four-valued logic for default reasoning to resolve the problems of inconsistency and incoherence and in the meantime retain classical extensions in the presence of consistency and coherency. The restricted semantics can maintain both the expressiveness and reasoning ability of default logic. We provide a transformation approach to compute the restricted extensions by reducing them into classical ones.     

Logical omniscience, semantics, and models of belief

Logical omniscience may be described (roughly) as the state of affairs in which an agent explicitly believes anything which is logically entailed by that agent's beliefs. It is widely agreed that humans are not logically omniscient, and that an adequate formal model of belief, coupled with a correct semantic theory, would not entail logical omniscience. Recently, two prominent models of belief have emerged which purport both to avoid logical omniscience and to provide an intuitively appealing semantics. The first of these models is due to Levesque (1984 b ); the second to Fagin and Halpem (1985). It is argued herein that each of these models faces serious difficulties. Detailed criticisms are presented for each model, and a computationally oriented theory of intensions is presented which provides the foundation for a new formal model of belief. This formal model is presented in a decidable subset of first-order logic and is shown to provide a solution to the general problem of logical omniscience. The model provides for the possibility of belief revision and places no a priori restrictions upon an agent's representation language.     

Metric semantics from partial order semantics

In dealing with denotational semantics of programming languages partial orders resp. metric spaces have been used with great benefit in order to provide a meaning to recursive and repetitive constructs. This paper presents two methods to define a metric on a subset of a complete partial order such that is a complete metric spaces and the metric semantics on coincides with the partial order semantics on when the same semantic operators are used. The first method is to add a ‘length’ on a complete partial order which means a function of increasing power. The second is based on the ideas of [11] and uses pseudo rank orderings, i.e. monotone sequences of monotone functions . We show that SFP domains can be characterized as special kinds of rank orderded cpo's. We also discuss the connection between the Lawson topology and the topology induced by the metric. Received 11 July 1995 / 1 August 1996     

Another perspective on default reasoning

The lexicographic closure of any given finite setD of normal defaults is defined. A conditional assertiona b is in this lexicographic closure if, given the defaultsD and the facta, one would concludeb. The lexicographic closure is essentially a rational extension ofD, and of its rational closure, defined in a previous paper. It provides a logic of normal defaults that is different from the one proposed by R. Reiter and that is rich enough not to require the consideration of non-normal defaults. A large number of examples are provided to show that the lexicographic closure corresponds to the basic intuitions behind Reiter's logic of defaults.This work was partially supported by the Jean and Helene Alfassa fund for research in artificial intelligence.     

Some Results on Default Logic

In the previous paper,some important properties of extensions of general default theories were given.In order to further explore default logic,a characterization of extensions is presented.And a class of defaults,so-called Auto-compatible Default Theory,is also introduced.All these essentially develop the theories of Reiter and his followers.     

基于语义的单文档自动摘要算法

单文档自动摘要的目的是在原始的文本中通过摘取、提炼主要信息,提供一篇简洁全面的摘要。自动摘要的主流方法是通过统计和机器学习的技术从文本中直接提取出句子,而单文档由于篇章有限,统计的方法无效。针对此问题,提出了基于语义的单文本自动摘要方法。该方法首先将文档划分为句子,然后计算每一对句子的语义相似度,通过运用改进型K-Medoids聚类算法将相似的句子归类,在每一类中选出最具代表性的句子,最后将句子组成文档摘要。实验结果表明,通过融合语义信息,该方法提高了摘要的质量。     

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.     

Emergent semantics

The article discusses ways to let semantics emerge from simple observations from the bottom-up, rather than imposing concepts on the observations top-down, to provide precise query, retrieval, communication or translation for a wide variety of applications. The following areas are examined: image retrieval and databases; media information spaces including the Semantic Web and MPEG frameworks; language games for emergent semantics; and emergent semantics for ontologies.     

Relation-algebraic semantics

The first half is a tutorial on orderings, lattices, Boolean algebras, operators on Boolean algebras, Tarski's fixed point theorem, and relation algebras.

In the second half, elements of a complete relation algebra are used as “meanings” for program statements. The use of relation algebras for this purpose was pioneered by de Bakker and de Roever in [10–12]. For a class of programming languages with program schemes, single μ-recursion, while-statements, if-then-else, sequential composition, and nondeterministic choice, a definition of “correct interpretation” is given which properly reflects the intuitive (or operational) meanings of the program constructs. A correct interpretation includes for each program statement an element serving as “input/output relation” and a domain element specifying that statement's “domain of nontermination”. The derivative of Hitchcock and Park [17] is defined and a relation-algebraic version of the extension by de Bakker [8, 9] of the Hitchcock-Park theorem is proved. The predicate transformers wp_s(-) and wlp_s(-) are defined and shown to obey all the standard laws in [15]. The “law of the excluded miracle” is shown to hold for an entire language if it holds for that language's basic statements (assignment statements and so on). Determinism is defined and characterized for all the program constructs. A relation-algebraic version of the invariance theorem for while-statements is given. An alternative definition of intepretation, called “demonic”, is obtained by using “demonic union” in place of ordinary union, and “demonic composition” in place of ordinary relational composition. Such interpretations are shown to arise naturally from a special class of correct interpretations, and to obey the laws of wp_s(-).     

Interactive semantics

Much research pursues machine intelligence through better representation of semantics. What is semantics? People in different areas view semantics from different facets although it accompanies interaction through civilization. Some researchers believe that humans have some innate structure in mind for processing semantics. Then, what the structure is like? Some argue that humans evolve a structure for processing semantics through constant learning. Then, how the process is like? Humans have invented various symbol systems to represent semantics. Can semantics be accurately represented? Turing machines are good at processing symbols according to algorithms designed by humans, but they are limited in ability to process semantics and to do active interaction. Super computers and high-speed networks do not help solve this issue as they do not have any semantic worldview and cannot reflect themselves. Can future cyber-society have some semantic images that enable machines and individuals (humans and agents) to reflect themselves and interact with each other with knowing social situation through time? This paper concerns these issues in the context of studying an interactive semantics for the future cyber-society. It firstly distinguishes social semantics from natural semantics, and then explores the interactive semantics in the category of social semantics. Interactive semantics consists of an interactive system and its semantic image, which co-evolve and influence each other. The semantic worldview and interactive semantic base are proposed as the semantic basis of interaction. The process of building and explaining semantic image can be based on an evolving structure incorporating adaptive multi-dimensional classification space and self-organized semantic link network. A semantic lens is proposed to enhance the potential of the structure and help individuals build and retrieve semantic images from different facets, abstraction levels and scales through time.     

Linking denotational semantics with operational semantics for web services

Web Services have become more and more important in these years, and BPEL4WS (BPEL) is a de facto standard for the web service composition and orchestration. It contains several distinct features, including the scope-based compensation and fault handling mechanism. The denotational semantics and operational semantics have been explored for BPEL. The two semantic models should be consistent. This paper considers the linking of these two semantics. Our approach is to derive the denotational semantics from operational semantics for BPEL, which aims for the consistency of the two models. Moreover, the derivation can be applied in exploring the program equivalence easily, especially for parallel programs.     

Formalizing Default Reasoning

Fuzzy set systems can be used to solve the problem with uncertain knowledge,and default logic can be used to solve the problem with incomplete knowledge,in some sense.In this paper,based on interval-valued fuzzy sets we introduce a method of inference which combines approximate reasoning an default ogic,and give the procedure of transforming monotonic reasoning into default reasoning.     

General default logic

In this paper, we propose a new nonmonotonic logic called general default logic. On the one hand, it generalizes Reiter’s default logic by adding to it rule-like operators used in logic programming. On the other hand, it extends logic programming by allowing arbitrary propositional formulas. We show that with this new logic, one can formalize naturally rule constraints, generalized closed world assumptions, and conditional defaults. We show that under a notion of strong equivalence, sentences of this new logic can be converted to a normal form. We also investigate the computational complexity of various reasoning tasks in the logic, and relate it to some other nonmonotonic formalisms such as Lin and Shoham’s logic of GK and Moore’s autoepistemic logic.     

Meaningful modeling: what's the semantics of "semantics"?

The Unified Modeling Language (UML) is a complex collection of mostly diagrammatic notations for software modeling, and its standardization has prompted an animated discussion about UML's semantics and how to represent it. We have thus set out to clarify some of the notions involved in defining modeling languages, with an eye toward the particular difficulties arising in defining UML. We are primarily interested in distinguishing a language's notation, or syntax, from its meaning, or semantics, as well as recognizing the differences between variants of syntax and semantics in their nature, purpose, style, and use.     

Reconciling statechart semantics

Statecharts are a visual technique for modelling reactive behaviour. Over the years, a plethora of statechart semantics have been proposed. The three most widely used are the fixpoint, Statemate, and UML semantics. These three semantics differ considerably from each other. In general, they interpret the same statechart differently, which impedes the communication of statechart designs among both designers and tools. In this paper, we identify a set of constraints on statecharts that ensure that the fixpoint, Statemate and UML semantics coincide, if observations are restricted to linear, stuttering-closed, separable properties. Moreover, we show that for a subset of these constraints, a slight variation of the Statemate semantics coincides for linear stuttering-closed properties with the UML semantics.