基于Petri网的TCP协议异常检测模型

从面向连接的角度出发，以Petri网为工具，建立了TCP协议异常检测模型．该模型以TCP协议的状态变迁图为基础，并根据协议规范可对传输报文的标志位进行系统的分析，从而识别出标志位非法组合构成的畸形报文（FIN—RST报文）．模型中规定了各种状态下可接收的标志位集合，同时还细化了各状态下的超时异常，据此可准确地检测出各种异常，以抵御已知和未知的非法行为．利用该模型不仅可发现已知异常事件，还可对未知漏洞进行防范．通过实验发现，网络中的错误标志位报文、端口扫描以及DOS攻击产生的异常流量将占到总流量的10%以上．     

Transition Specifications for Dynamic Abstract Data Types

Transition specifications extend algebraic specifications by a notion of states and state transitions, introducing a second dynamic layer on abstract data types. This makes possible a reduction of complex specifications by the introduction of an explicit system state, a formal comparison of algebraic specifications and imperative algorithms, and the specification of input/output and other communication features. States are modelled as partial algebras that extend a given algebra by an environment, that is, a partial function that assigns contents to references. State transitions are specified by conditional parallel assignments, analoguous to the conditional existence equations of partial equational specifications. A framework of transition specifications is developed, including initial model semantics, parameterization and general composition mechanisms, and a notion of model correctness. Examples from programming languages show the applicability of the approach.     

微机仿真系统中形式化方法的应用

Z语言是一种广泛应用的形式化语言，适合于仿真实时软件系统的需求规格说明．通过微机系统仿真软件的Z规格说明，讨论了Z语言在实时系统开发中使用的一些方法、对典型问题的处理原则以及操作同时序关系的描述．     

Specification on the interval

We study the consequences of discontinuities on the specification property for interval maps. After giving a necessary and sufficient condition for a piecewise monotonic, piecewise continuous map to have this property, we show that for a large and natural class of families of such maps (including the -transformations), the set of parameters for which the specification property holds, though dense, has zero Lebesgue measure. Thus, regarding the specification property, the general case is at the opposite of the continuous case solved by A.M. Blokh (Russian Math. Surveys 38 (1983), 133-134) (for which we give a proof).

     

真拟弱几乎周期点和拟正则点

T为紧致度量空间X上的连续映射,M（X）为X上所有Borel概率测度.设x∈X,记Mx（T）为概率测度序列{1n∑n 1i=0δTi（x）}在M（X）中的极限点的集合,其中δx表示支撑集是{x}的点测度.记W（T）和QW（T）分别为T的弱几乎周期点和拟弱几乎周期点集.本文证明,如果（X,T）非平凡且满足specifcation性质,则存在x,y∈QW（T）／W（T）（称为真拟弱几乎周期点）,分别满足μ∈Mx（T）,x∈Supp（μ）和ν∈My（T）,y∈/Supp（ν）,回答了周作领等提出的公开问题.Mx（T）在弱拓扑中是紧致连通集,所以,要么是单点集,要么是不可数集.如果x∈QW（T）／W（T）,则Mx（T）是不可数集.一个自然的问题是,怎么刻画M x（T）是单点集的点x（这时x称为拟正则点）.本文给出M x（T）是单点集的充要条件.     

汉语“规范”及“标准”等词语的英文表达法

＂Code＂、＂Standard＂以及＂Specification＂等词语在科技英语中经常出现。在大多数情况下,＂规范＂、＂标准＂在施工、设计和验收等方面才会用到。在实际运用中,我们还需灵活掌握这些词语,以更好地表达出原文的意思。     

MRPII系统开发的一种形式化方法

研究了ＭＲＰＩＩ系统开发的形式化方法。使用形式化语言ＲＳＬ定义ＭＲＰＩＩ系统的规范和精化关系。以库存管理子模块为例，详细介绍了将形式化方法ＲＡＩＳＥ应用于ＭＲＰＩＩ系统的规范、精化、验证和实现。     

关于呼延水厂绿化的思考

结合绿化建设工作实际,提出应当通过大树移植,大面积种植草坪,爬山虎、合欢、火炬等苗木的选择,苗木名称细化,经济林木的选取等措施对呼延水厂园林进行绿化。     

Past–future separation and normal forms in temporal predicate logic specifications

Temporal specifications are often used when phenomena are modelled where dynamics play a main role. If simulation is one of the aims of modelling, usually a restricted, executable modelling language format is used, based on some form of past to future implications. In this paper a detailed transformation procedure is described that takes any temporal predicate logic specification and generates a specification in a past-implies-future normal format. The procedure works for temporal specifications in which the atoms either express time ordering relations or are state-related, i.e., include only one time variable.     

形式化方法在核事故评价系统中的应用

核事故评价系统针对核事故发生后第一时间对其进行评价和预测分析,软件可靠性要求高.形式化方法具有严格数学基础,是软件开发最为重要的理论工具.本文首先用UML对系统进行分析建模,采用形式化语言对系统功能进行严格规约描述,提高系统开发的可靠性.