XMLS指XML Schema，即XML模式，用于定义XML词表和结构用于机器识别和共享信息的定义语言。
Express shared vocabularies and allow machines to carry out rules made by people. They provide a means for defining the structure, content and semantics of XML documents. [W3C consortium "XML schema"] http://www.w3.org/XML/Schema
XML Schema is a language for describing the structure and constraining the contents of XML documents