XML schema的用法
XML Schema是以XML语言为基础的,它用于可替代DTD。
一份XML schema文件描述了XML文档的结构。
XML Schema语言也被称为XML Schema Definition (XSD)(XML Schema定义).
1.什么是XML Schema?
XML Schema的作用是定义一份XML文档的合法组件群,就像DTD的作用一样,一份XML Schema:
定义了可以出现在文档里的元素
定义了可以出现在文档里的属性
定义了哪些元素是子元素
定义了子元素的顺序
定义了子元素的数量
定义了一个元素应是否能包含文本,或应该是空的
定义了元素和属性的数据类型
定义了元素和属性的默认值和固定值
2.XML Schema 是DTD的“接任者”
我们认为XML Schema很快就会替代DTD在大多数的网络应用程序中被广泛使用。
XML Schema针对将来的额外内容是可扩展的
XML Schema内容比DTD丰富,作用也更大
XML Schema是以XML语言编写而成的
XML Schema支持数据类型
XML Schema支持名称空间(namespaces)
3.XML Schema是W3C定义的标准
XML Schema于2001年5月2日成为W3C推荐使用的标准
在W3C 教程中你能阅读到更多关于XML Schema标准。
例如,我可以定义一个student的xml文档如下:
这是一个schema 文档的定义 student.xsd
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下面添加一个xml文件来引用这个schema:student.xml
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这时候当出现任何一个子元素与定义的不同时,就会报错。