DTD 属性基础概念DTDDocument Type Definition中属性的定义用于为元素添加额外信息。属性通过!ATTLIST声明包含元素名称、属性名称、属性类型和默认值。属性声明语法!ATTLIST element_name attribute_name attribute_type default_value属性类型示例CDATA类型字符数据不包含标记!ATTLIST person name CDATA #REQUIRED对应XMLperson name张三/枚举类型限定属性值为特定选项!ATTLIST car color (red|blue|black) red对应XMLcar colorblue/ID类型唯一标识符!ATTLIST student id ID #REQUIRED对应XMLstudent ids1001/属性默认值#REQUIRED必须提供属性值!ATTLIST book isbn CDATA #REQUIRED#IMPLIED属性可选!ATTLIST product discount CDATA #IMPLIED固定值默认值固定!ATTLIST company type CDATA IT复杂属性示例多属性声明!ATTLIST image src CDATA #REQUIRED width CDATA #IMPLIED height CDATA #IMPLIED alt CDATA #REQUIRED对应XMLimage srclogo.png altCompany Logo width200/IDREF类型引用其他元素的ID!ATTLIST order customer IDREF #REQUIRED !ATTLIST customer id ID #REQUIRED对应XMLcustomer idc001/ order customerc001/实体与属性结合ENTITY类型引用外部实体!ENTITY logo SYSTEM logo.png !ATTLIST company logo ENTITY #REQUIRED对应XMLcompany logologo/NMTOKEN类型限制为有效名称字符!ATTLIST user login NMTOKEN #REQUIRED对应XMLuser loginjohn_doe/综合DTD示例完整DTD文件示例!ELEMENT bookstore (book) !ELEMENT book (title,author,price) !ATTLIST book id ID #REQUIRED category (fiction|nonfiction) #REQUIRED lang CDATA #IMPLIED !ELEMENT title (#PCDATA) !ELEMENT author (#PCDATA) !ELEMENT price (#PCDATA)对应XML实例bookstore book idb101 categoryfiction langen titleThe Great Novel/title authorJohn Smith/author price29.99/price /book /bookstore属性使用注意事项属性值必须用引号包围单引号或双引号均可product codeP-1001 descPremium Quality/避免过度使用属性对于复杂数据应使用元素!-- 不推荐 -- person name李四 age30 address北京/ !-- 推荐 -- person name李四/name age30/age address北京/address /person