任意包含参数或者其他元素得元素是复杂类型元素。
例子：
<xsd:element name="shirt">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="color" type="xsd:string"/>
<xsd:element name="size" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
//<xsd:sequence> 里的元素只能出现一次，而且要符合顺序
xml文件：
<shirt>
<color>purple</color>
<size>XL</size>
</shirt>
设置元素的出现次数
<xsd:element name="completeOrder">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="shirt" minOccurs="0" maxOccurs="unbounded" type="xsd:string" />
<xsd:element name="sweatshirt" minOccurs="0" maxOccurs="unbounded" type="xsd:string" />
<xsd:element name="mugs" minOccurs="0" maxOccurs="100" type="xsd:string" />
<xsd:element name="hats" minOccurs="0" maxOccurs="50" type="xsd:string" />
</xsd:sequence>
</xsd:complexType>
</xsd:element>
使用参数minOccurs="0" 和 maxOccurs="unbounded" 可以控制元素出现的次数
xml文件：
<completeOrder>
<shirt>9 purple X</shirt>
<shirt>3 blue S</shirt>
<shirt>11 orange XXL</shirt>
<sweatshirt>19 green</sweatshirt>
<mugs>8 porcelain</mugs>
</completeOrder>
比较XML Schema 和 DTD (设置元素出现次数)
XML Schema DTD
minOccurs="0"
maxOccurs="unbounded" element*
minOccurs="0"
maxOccurs="1" element?
minOccurs="1"
maxOccurs="unbounded" element+
Default:
minOccurs="1"
maxOccurs="1" element
学习xsd: choice
<xsd:element name="singleItemOrder">
<xsd:complexType>
<xsd:choice>
<xsd:element name="shirt" type="xsd:string" />
<xsd:element name="sweatshirt" type="xsd:string"/>
<xsd:element name="mugs" type="xsd:integer"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>
在choice中的元素选项中只能选一个
学习xsd:all
<xsd:element name="completeOrder">
<xsd:complexType>
<xsd:all>
<xsd:element name="shirt" type="xsd:string" minOc-curs="0" maxOccurs="unbounded"/>
<xsd:element name="sweatshirt" type="xsd:string" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element name="mugs" type="xsd:string" minOc-curs="0" maxOccurs="100"/>
<xsd:element name="hats" type="xsd:string" minOc-curs="0" maxOccurs="50"/>
</xsd:all>
</xsd:complexType>
</xsd:element>
在all中的元素不考虑顺序，但是sequence中顺序是固定的