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。