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FTP服务器枢纽中的文件处理引擎设计   总被引：3，自引：0，他引：3       下载免费PDF全文

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Mathematical expressions in tabular form (also called “tabular expressions” or “tables”) have been shown to be useful for documenting and analysing software systems. They are usually easier to read than conventional mathematical expressions but are no less precise. They can be used wherever mathematical expressions are used. To avoid misunderstandings, and to support users with trustworthy tools, the meaning of these expressions must be fully defined.This paper presents a new method for defining the meaning of tabular expressions. Each definition of an expression type names the expression’s constituents, and provides a restriction schema and one or more evaluation schemas. The restriction schema defines the class of well-formed expressions of the type. An evaluation schema maps a well-formed tabular expression of the type to a mathematical expression of a previously defined type. Since the meaning of conventional mathematical expressions is well known, describing an equivalent expression fully defines the meaning of a tabular expression.In this approach, indexation is used to decouple the appearance of a tabular expression from its semantics. A tabular expression is an indexed set of grids; a grid is an indexed set of expressions. The expressions in a grid can be either conventional expressions or tabular expressions of a previously defined type.Defining the meaning of a tabular expression in this way facilitates the building of tools that faithfully implement the semantics. The decoupling of syntax and semantics by means of indices overcomes some limitations of older approaches.The method presented in the paper is illustrated by defining several previously known types of tabular expressions and some new ones. The use of the new model to build a suite of tools for the input, presentation, validation, evaluation, simplification, conversion and composition of tabular expressions is discussed.  相似文献
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Tabular 表达式是一种采用表格化结构组织函数或关系的形式化描述工具，在需求工程领域中具有广泛的应用，为Tabular 表达式建立形式的语义模型是非常必要的.针对Tabular 表达式通用模型，给出了Tabular 表达式的形式文法及指称语义.通过定义形式文法中各语法单元的语义指派方程，描述了Tabular 表达式的指称语义，分别对传统类型Tabular 表达式和新类型Tabular 表达式中一些典型表类型的指称语义进行了描述，并与其他几种Tabular 表达式的语义描述方法进行了比较.分析结果表明：该语义描述方法不仅准确描述了Tabular 表达式的语义，而且不再受Tabular 表达式模型和Tabular 表达式类型的限制，打破了现有方法的局限性，是一种非常有效的方法.  相似文献
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