基于时序描述逻辑的UML顺序图形式化研究

在统一建模语言（UML）规范中顺序图的语义是以自然语言的形式描述的,是一种半形式化的语言,不能对系统的交互行为进行形式化分析及论证.针对UML顺序图缺乏精确的形式化描述问题,根据顺序图的时序特征,提出了增加交互操作符的UML顺序图的六元组形式化方法.对描述逻辑进行时序扩展,得到可表示动态和时序语义的形式化规范——时序描述逻辑.应用时序描述逻辑的时态算子得到时序描述逻辑语义形式的UML顺序图.用UML顺序图描述完整的C语言执行过程,将其形式化描述,实验结果表明,这种方法是可行的.     

UML顺序图的结构化操作语义研究

UML顺序图侧重于展示对象之间的消息交互过程,但其动态语义缺乏形式化的描述,不利于对顺序图模型的准确理解和基于该模型的测试用例生成。为此,依据UML1. 5规范,采用BN定义顺序图的形式化语法,提出了活动点的概念;在此基础上,讨论并给出了单个对象执行消息动作的结构化操作语义以及顺序图模型的整体结构化操作语义,为模型检验和基于顺序图的测试用例生成提供了前提。     

UML2.0顺序图的形式化研究

在UML2.0规范中顺序图的语义仍然是以自然语言的形式描述的,为实现对顺序图的自动化分析和验证,必须为顺序图定义一种形式化的语义模型.为此首先给出了UML顺序图的一种符合BNF范式的形式化语法,然后为该语法中的非终止符定义转换规则,将UML顺序图中的基本动作转换为加标Petri网组件,最后定义了各种合成操作,利用这些合成操作可以将UML顺序图的加标Petri网组件转换为加标Petni网.     

UML2.0顺序图的时序描述逻辑语义

针对UML2.0顺序图用于对象间交互行为建模时存在动态语义缺乏精确形式化描述的问题,提出一种基于时序描述逻辑的UML2.0顺序图形式化方法。对描述逻辑进行时序扩展,得到可表示动态和时序语义的形式化规范——时序描述逻辑,根据UML2.0新增的交互操作符将UML2.0顺序图分成一个或多个最大顺序片段,通过形式化最大顺序片段和交互操作符得到UML2.0顺序图的时序描述逻辑语义。实例检验结果表明,该方法具有可行性。     

UML活动图的操作语义

越来越多的系统采用UML（unified model language,统一建模语言）作为建模语言来进行系统分析和设计.UML活动图是UML语言中描述系统动态行为的一种方法,它广泛地运用于业务建模.由于UML活动图缺乏精确的动态语义,所以不利于对其所描述的系统进行形式化的分析、验证和确认.为解决这一问题,根据UML1.5语义文档,给出UML活动图的形式化操作语义.首先给出UML活动图的形式化的语法,然后详细地定义了活动图的格局和变迁,最后基于LTS给出了活动图的演绎规则.主要工作是：引入状态包的概念,使得描述更加清楚、完善;通过LTS定义活动图的操作语义,并详细阐述演绎规则,从而获得活动图的全局状态转移图,使定义的操作语义很容易地应用到形式化验证中.该语义覆盖了UML活动图的绝大部分特征,为对UML活动图进行模型检验奠定了基础.     

UML活动图的形式语义及分析

UML活动图缺乏精确的动态语义,不利于对其所描述的系统进行形式化的分析、验证和确认。为此,论文结合Petri网给出了包含对象流状态描述的UML活动图的形式语义,并据此对UML活动图的典型流程和其所描述的动态系统的正确性进行了分析。该形式语义覆盖了UML活动图的绝大部分特征,为精确描述工作流程并对其进行分析奠定了基础。     

一种基于CSP的面向方面状态图形式化描述方法

面向方面通过分离关注点解决软件系统中的横切问题,通过扩展UML可实现对面向方面的建模。本文利用UML的扩展机制将方面加入状态图中,描述了状态图中的方面与核心组件以及方面之间的编织,然后利用进程代数的形式化语义描述了扩展后的UML状态图,克服了扩展UML描述状态图的缺乏形式化动态语义,不利于对模型进行形式化验证和证明的缺
点。最后,以ATM自动取款机为例验证了基于CSP的面向方面状态图形式化描述的有效性。     

关于UML顺序图的结构化操作语义描述的研究

UML规范本身因为描述语言的限制,所以在语义方面有其模糊和难以把握的地方。本文使用结构化操作语义,对其顺序图做了形式化的描述。     

UML模型形式化B方法转换的实现

UML是软件开发的标准语言,已经广泛运用于各种领域的软件设计建模之中。但是UML的半形式化表达方式缺乏准确的语义,使其无法在软件设计过程中针对需求的一致性进行分析,因此需要使用一种形式化方法对UML模型进行描述。以高速列车控制系统为例,基于B方法对用例图模型与顺序图模型进行形式化转换,对两种模型中各组成部分从语义角度分别进行了描述,从而完整地刻画了UML模型所描述的系统需求。     

基于时序逻辑的UML2.0通信图语义研究

UML2.0通信图可以表示对象之间的交互,很适合用于对系统的交互行为建模,但由于UML缺乏精确语义,使得难以对其所表示的系统行为进行分析和验证.XYZ/E是可执行线性时序逻辑语言,既可描述系统的静态语义和动态语义.在定K.UML2.0通信图的形式化语法的基础上,给出了通信图的XYZ/E时序逻辑语义,为进一步的系统分析和验证提供了形式化基础.     

Transfinite Semantics in the Form of Greatest Fixpoint

Transfinite semantics is a semantics according to which program executions can continue working after an infinite number of steps. Such a view of programs can be useful in the theory of program transformations.So far, transfinite semantics have been succesfully defined for iterative loops. This paper provides an exhaustive definition for semantics that enable also infinitely deep recursion.The definition is actually a parametric schema that defines a family of different transfinite semantics. As standard semantics also match the same schema, our framework describes both standard and transfinite semantics in a uniform way.All semantics are expressed as greatest fixpoints of monotone operators on some complete lattices. It turns out that, for transfinite semantics, the corresponding lattice operators are cocontinuous. According to Kleene’s theorem, this shows that transfinite semantics can be expressed as a limit of iteration which is not transfinite.     

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     

A compact fixpoint semantics for term rewriting systems

This work is motivated by the fact that a “compact” semantics for term rewriting systems, which is essential for the development of effective semantics-based program manipulation tools (e.g. automatic program analyzers and debuggers), does not exist. The big-step rewriting semantics that is most commonly considered in functional programming is the set of values/normal forms that the program is able to compute for any input expression. Such a big-step semantics is unnecessarily oversized, as it contains many “semantically useless” elements that can be retrieved from a smaller set of terms. Therefore, in this article, we present a compressed, goal-independent collecting fixpoint semantics that contains the smallest set of terms that are sufficient to describe, by semantic closure, all possible rewritings. We prove soundness and completeness under ascertained conditions. The compactness of the semantics makes it suitable for applications. Actually, our semantics can be finite whereas the big-step semantics is generally not, and even when both semantics are infinite, the fixpoint computation of our semantics produces fewer elements at each step. To support this claim we report several experiments performed with a prototypical implementation.     

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).     

There is no fully abstract fixpoint semantics for non-deterministic languages with infinite computations

It is well known that for many non-deterministic programming languages there is no continuous fully abstract fixpoint semantics. This is usually attributed to “problems with continuity”, that is, the assumption that the semantic functions should be continuous supposedly plays a role in the difficulties of giving a fully abstract fixpoint semantics. We show that for a large class of non-deterministic programming languages there is no fully abstract least fixpoint semantics even if one considers arbitrary functions (not necessarily continuous) over arbitrary partial orders (not necessarily complete).     

A survey on socio-semantic information retrieval

The rise of the Social Web and advances in the Semantic Web provides unprecedented possibilities for the development of novel methods to enhance the information retrieval (IR) process by including varying degrees of semantics. We shed light on the corresponding notion of semantically-enhanced information retrieval by presenting state-of-the art techniques in related research areas. We describe techniques based on the main processes of a typical IR workflow and map them onto three main types of semantics, which vary from formal semantic knowledge representations and content-based semantics to social semantics emerging through usage and user interactions.     

基于图像语义模型识别的道路汽车跟踪

在道路汽车跟踪算法研究中,论文提出了基于场景和运动主体模型的目标跟踪法,通过提取道路与汽车的高层信息属性,建立基于主体运行知识结构与操作方法的语义模型,实施对汽车的运动跟踪。这种目标跟踪算法体现了主体运行意图和操作的知识表达,丰富了目标跟踪算法的研究。     

Bi-inductive Structural Semantics: (Extended Abstract)

We propose a simple order-theoretic generalization of set-theoretic inductive definitions. This generalization covers inductive, co-inductive and bi-inductive definitions and is preserved by abstraction. This allows the structural operational semantics to describe simultaneously the finite/terminating and infinite/diverging behaviors of programs. This is illustrated on the structural bifinitary small/big-step trace/relational/operational semantics of the call-by-value λ-calculus.