计算机经典英语短文阅读

计算机英语一 CMS is used to digitally sign or encrypt arbitrary messages. CMS describes an encapsulation syntax for data protection. It supports digital signatures and Encryption. The syntax allows multiple encapsulation, so one encapsulation envelope can be nested inside another. Likewise, one party can digitally sign some previously encapsulated data. It also allows arbitrary attributes, such as signing time, to be authenticated along with the message content, and provides for other attributes such as countersignatures to be associated with a signature. CMS 被用于数据签名或者任意消息加密中。CMS 提供了一套用于数据 保护的数据封装语法。该语法支持数据签名和数据加密。该语法允许多重封 装，所以一封数据信封能被另外一封数据信封所封装。同样的，该语法封装 数据的部分数据位可以用来表示被封装数据。也允附加一些属性如签名时间 ， 它和内容信息一起用于鉴别信息;计数器属性，它为其它属性提供计数信息。 计算机英语二 XDM is the foundation of XPath 2.0 and defines the Data Model for XPath 2.0 (and consequently XQuery 1.0 and XSLT 2.0, which are both based on XPath 2.0). XDM is built on top of the XML Info set (the abstraction of an XML document), PSVI (type annotations in the XML Info set as the result of XML Schema validation), the simple data types of XML Schema, and additional concepts. The most important additional concept is that of a "sequence", which embraces both simple data types and the XML-derived nodes. XDM 是 XPath2.0 的基础，它定义了 XPath2.0 的数据模型(因此 XQuery 1.0 、XSLT 2.0 也就基于 XPath 2.0)。XDM 建立在 XML 信息集(从 XML 文档 中抽取)和 PSVI(作为确认 XML Schema 结果的 XML 信息集合的注释类型)的 顶端、属于简单的 XML Schema 的数据类型、是一个附加的概念。其中，它 最重要的附加概念就是“顺序”，即包括简单数据类型和 XML 的源节点。 计算机英语三 Internet technical specifications often need to define a format syntax and are free to employ whatever notation their authors deem useful. Over the years, a modified version of BNF, called ABNF, has been popular among many Internet specifications. It balances compactness and simplicity with reasonable representational power. 互联网技术规范经常需要定义一种格式化语法并能自由地使用作者认为 是有用的任何符号。多年来，巴克斯范式(BNF)的一个修订版，即扩展巴克 斯范式(ABNF)，已经在许多互联网规范中流行。该版本平衡了压缩性和简单 性，具有合理的表达能力。