一种改进的布尔表达式自下而上分析的语法制导翻译的方法

本文针对文献[1]中布尔表达式文法和语义子程序不能适用于算法优先分析的语法制导翻译法的局限,从算符优先分析法和语法制导翻译的定义及本质特点出发,提出了一种改进方法,实现了算符优先分析制导翻译布尔表达式。     

关系代数派生算子语义表达式间等价性证明

关系代数的派生算子在关系数据库查询语言中得到了广泛应用。它们的语义有两种常见的表示方式,一种是基于原始算子的表达式,一种是基于一阶逻辑的表达式。但有关的文献资料都没有给出这两种表达式等价性的严格证明。文章尝试通过一系列等价变换,证明派生算子语义的这两种表达式间的等价性。从派生算子(主要是除算子)语义的原始算子表达式出发,根据关系代数表达式的特点,通过一步步的等价变换,得到派生算子语义的一阶逻辑表达式。所使用的变换方法能为关系代数表达式的正确性证明打下基础。     

关系代数派生算子语义表达式间等价性证明

关系代数的派生算子在关系数据库查询语言中得到了广泛应用。它们的语义有两种常见的表示方式,一种是基于原始算子的表达式,一种是基于一阶逻辑的表达式。但有关的文献资料都没有给出这两种表达式等价性的严格证明。文章尝试通过一系列等价变换,证明派生算子语义的这两种表达式间的等价性。从派生算子（主要是除算子）语义的原始算子表达式出发,根据关系代数表达式的特点,通过一步步的等价变换,得到派生算子语义的一阶逻辑表达式。所使用的变换方法能为关系代数表达式的正确性证明打下基础。     

合成语言FOPL基于方程逻辑的语义

程序设计语言ＦＯＰＬ是一种同时支持函数式程序设计风洛和面向对象程序设计风格的合成语言．本义介绍了ＦＯＰＬ的类型思想，并讨论了表达式纯洁性判断规则、表达式附类型规则及表达式等价判断规则，这些规则描述了ＦＯＰＬ基于方程逻辑的语义．     

几种路径表达式及其在分布环境下的实现技术

路径表达式(path expression)是一种非过程化的共享资源并发存取控制的描述语言。本文介绍它们的几种形式:断言路径表达式(Predicate pathexpression)、开放路径表达式(Open path expression)、开放断言路径表达式(Open predicate path expression),主要介绍它们的语法、语义和实现技术。并对它们的特点、表达能力等进行了讨论。结论是路径表达式是一种适合于分布环境的高级同步描述工具。     

形式语义学发展简介

一.前言最近十年,形式描述和说明技术有了迅速发展。从对程序设计语言的形式描述来说,最初的一次正规、严格的形式描述是Algol 60的文法描述,接着 IBM 的研究人员对 PL/I 的文法和语义作了严格的形式描述,Wirth 也和 Hoare 合作对其杰作 PASCAL 语言作了公理化语义描述,目前又发表了对 Ada 的形式描述。形势是,一种程序语言的推出,若无严格的形式(文法与语义)定义,似乎无法叫人信赖。与此同时,对各     

应用双带产生式进行并行代码生成

本文基于ＹＨ－Ｆ２系统编译程序设计,为最大程度地开发ＹＨ－Ｆ２对复杂算术表达式的并行计算能力,引入二次文法及双带产生式系统描述算术表达式,并据此设计双带产生式的ＳＬＲ制导翻译方法,对复杂表达式进行并行代码生成,取得了圆满的效果。     

Petri网的进程表达式与语言表达式

Petri网的语言和进程都是网系统行为的一种有效的描述手段,对应的进程表达式和语言表达式给出了系统全体行为的约束描述．本文首先对Petrl网的进程表达式进行了类型的划分并给出了相应的代数判定依据，随后证明了Petri网的进程表达式与语言表达式的类型一致性，由此给出了由进程表达式求取语言表达式的算法，为基于Petri网语言(尤其是无界Petri网)分析实际的物理系统提供了更为有效的途径．     

vCGG:一种基于虚结点的空间图文法形式框架

作为一种二维的形式化方法,图文法为可视化语言提供了直观而规范的描述手段.然而,大多数图文法形式框架在空间语义处理能力方面有所不足,影响了图文法的表达能力及其实际应用范围.针对现存的问题,构建了一种新型空间图文法形式框架vCGG （virtual-node based coordinate graph grammar）.区别于其他空间图文法,vCGG在产生式中通过定义虚结点的概念描述产生式与主图之间的语法结构与空间语义关系,在保留抽象能力的同时,提高了其空间语义配置性能.通过与几种典型空间图文法框架比较,vCGG形式框架在直观性、规范性、表达能力以及分析效率方面均有着较好的表现.     

语义转换--直接指称语义到接续指称语义

指称语义分为直接指称语义和接续指称语义，其中后一种语义描述的难度较大，给出了直接指称语义描述到接续指称语义描述的转换方法，这就使得这种语义转换的自动化成为可能．转换算法揭示了直接指称语义与接续指称语义之间的内在关系，同时也提供了写接续指称语义描述的有效方法．当需要检验同一种语言的直接指称语义描述和接续指称语义描述是否等价时，提供的技术是很有用的。     

The formal definition of a real-time language

Summary This paper presents the formal definition of TOMAL (Task-Oriented Microprocessor Applications Language), a programming language intended for real-time systems running on small processors. The formal definition addresses all aspects of the language. Because some modes of semantic definition seem particularly well-suited to certain aspects of a language, and not as suitable for others, the formal definition employs several complementary modes of definition.The primary definition is axiomatic and is employed to define most statements of the language. Simple, denotational (but not lattice-theoretic) semantics complement the axiomatic semantics to define type-related features, such as binding of names to types, data type coercions, and evaluation of expressions. Together, the axiomatic and denotational semantics define all features of the sequential language. An operational definition is used to define real-time execution, and to extend the axiomatic definition to account for all aspects of concurrent execution. Semantic constraints, sufficient to guarantee conformity of a program with the axiomatic definition, can be checked by analysis of a TOMAL program at compilation.     

Circular expressions: elimination of static environments

Consider the connection between denotational semantics for a language with goto statements and flow diagrams for programs in such a language. The main point of interest is that the denotational semantics uses a recursively defined environment to give the meaning of labels, while a flow diagram merely has a jump to the appropriate program point. A simple reduction called “indirection elimination” strips away the environment from the denotational semantics and extracts an expression with cycles that is very close to the flow diagram of a program. The same idea applies to associating bodies with recursive procedures, or to any construct whose semantics is not wedded to the syntax. In addition to being a useful data structure and conceptual device, expressions with cycles are well defined mathematical objects—their semantics can be given by unfolding them into infinite structures that have been well studied. The practicality of the elimination of environments has been tested by constructing a trial implementation, which serves as the front end of a semantics directed compiler generator. The implementation takes a denotational semantics of a language and constructs a “black box” that maps programs in the language into an intermediate representation. The intermediate representation is a circular expression.     

Optimizing Queries with Object Updates

Object-oriented databases (OODBs) provide powerful data abstractions and modeling facilities but they usually lack a suitable framework for query processing and optimization. Even though there is an increasing number of recent proposals on OODB query optimization, only few of them are actually focused on query optimization in the presence of object identity and destructive updates, features often supported by most realistic OODB languages. This paper presents a formal framework for optimizing object-oriented queries in the presence of side effects. These queries may contain object updates at any place and in any form. We present a language extension to the monoid comprehension calculus to express these object-oriented features and we give a formal meaning to these extensions. Our method is based on denotational semantics, which is often used to give a formal meaning to imperative programming languages. The semantics of our language extensions is expressed in terms of our monoid calculus, without the need of any fundamental change to our basic framework. Our method not only maintains referential transparency, which allows us to do meaningful query optimization, but it is also practical for optimizing OODB queries since it allows the same optimization techniques applied to regular queries to be used with minimal changes for OODB queries with updates.     

一种时态数据形式语言模型

数据模型是数据库技术发展的主线,时态数据模型是时态数据库系统的核心与基础。针对时态数据模型的研究现状,初步探讨了时态数据模型的基本要素,建立了一种形式化时态数据模型;基于形式语言理论和形式语义学的指称语义方法,进一步建立了该时态数据模型的形式语言模型。应用时态数据形式语言模型定义了各类时态完整性约束的形式语义规则,深入分析了时态数据模型内在的时态语义联系,为时态数据模型的研究提供了一个便利、高效的形式化理论框架。     

Smalltalk－80的指称语义研究

Ｓｍａｌｌｔａｌｋ—８０是原型的面向对象程序设计语言和环境．本文简要地给出了Ｓｍａｌｌｔａｌｋ－８０的形式模型，并基于该模型描述了Ｓｍａｌｌｔａｌｋ—８０的静态和动态指称语义．     

A fixpoint semantics of Horn sentences based on substitution sets

The formal semantics of a given Horn sentence is usually defined as a set of ground atoms, which is really the minimal Herbrand interpretation of the Horn sentence, by both model-theoretic and fixpoint approaches. In the present paper, we propose another denotational semantics of a Horn sentence, denoting the set of substitutions with which atoms are derivable by unit deduction from the Horn sentence to get a direct correspondence between the semantics of the Horn sentence and the answer set concerned with its computation, and give denotational semantics even when the Horn sentence is unsatisfiable. In accordance with the unit deductions from a Horn sentence, we define a continuous function from a direct product of powersets of a substitution set to itself, and regard the least fixpoint of the function as the semantics, which can provide the answer set for computations of the Horn sentence.     

Event-based operational semantics and a consistency result for real-time concurrent processes with action refinement

In this paper an event-based operational interleaving semantics is proposed for real-time processes,for which action refinement and a denotational true concurrency semantics are developed and defined in terms of timed event structures. The authors characterize the timed event traces that are generated by the operational semantics in a denotational way, and show that this operational semantics is consistent with the denotational semantics in the sense that they generate the same set of timed event traces, thereby eliminating the gap between the true concurrency and interleaving semantics.     

Semantics of under-determined expressions

Some specification languages, such as VDM-SL, allow expressions whose values are not fully determined. This may be convenient in cases where the choice of value should be left to a later stage of development.We consider a simple functional language including such under-determined expressions and present a denotational semantics for the language along with a set of proof rules for reasoning about properties of under-determined expressions. One of the specific problems considered is the combination of under-determinedness and a least fixed point semantics of recursion. Soundness of the proof rules is also discussed.