Composite Element sa XSD

复合元素包含了其他的元素及/或属性。

什么是复合元素？

复合元素指包含其他元素及/或属性的 XML 元素。

有四种类型的复合元素：

  • 空元素
  • 包含其他元素的元素
  • 仅包含文本的元素
  • 包含元素和文本的元素

注释：上述元素均可包含属性！

复合元素的例子

复合元素，"product"，是空的：

<product pid="1345"/>

复合元素，"employee"，仅包含其他元素：

<employee>
<firstname>John</firstname>
<lastname>Smith</lastname>
</employee>

复合元素，"food"，仅包含文本：

<food type="dessert">Ice cream</food>

复合元素，"description"，包含元素和文本：

<description>
It happened on <date lang="norwegian">03.03.99</date> ....
</description>

如何定义复合元素？

请看这个复合 XML 元素，"employee"，仅包含其他元素：

<employee>
<firstname>John</firstname>
<lastname>Smith</lastname>
</employee>

在 XML Schema 中，我们有两种方式来定义复合元素：

1. 程序名此元素，可直接对"employee"元素进行声明，就像这样：

<xs:element name="employee">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="firstname" type="xs:string"/>
      <xs:element name="lastname" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

Kung gamit mo ang inilarawan na pamamaraan, makakakuha ka lamang ng "employee" na pwedeng gamitin ang tinukoy na compound type. Mangyaring paniwalaan ang mga anak na elemento, "firstname" at "lastname", na nasa loob ng tagapagpahiwatig <sequence>. Ito ay nangangahulugan na ang mga anak na elemento ay dapat lumitaw sa pagkakasunod-sunod na kanilang pinangalanan. Makikita mo ito sa Tagapagpahiwatig ng XSD Ito ang aral sa mas maraming kaalaman tungkol sa mga tagapagpahiwatig.

2. "employee" na elemento ay pwedeng gamitin ang attribute na type, na ginagamit upang tumutukoy sa pangalan ng compound type na gagamitin:

<xs:element name="employee" type="personinfo"/>
<xs:complexType name="personinfo">
  <xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
  </xs:sequence>
</xs:complexType>

Kung gamit mo ang inilarawan na pamamaraan, maaaring gamitin ng ilang elemento ang parehong compound type, tulad nito:

<xs:element name="employee" type="personinfo"/>
<xs:element name="student" type="personinfo"/>
<xs:element name="member" type="personinfo"/>
<xs:complexType name="personinfo">
  <xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
  </xs:sequence>
</xs:complexType>

Maaari ka ring magdagdag ng ilang elemento sa eksistensyang compound element sa pamamagitan ng paggamit ng isang compound element bilang batayan, tulad nito:

<xs:element name="employee" type="fullpersoninfo"/>
<xs:complexType name="personinfo">
  <xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
  </xs:sequence>
</xs:complexType>
<xs:complexType name="fullpersoninfo">
  <xs:complexContent>
    <xs:extension base="personinfo">
      <xs:sequence>
        <xs:element name="address" type="xs:string"/>
        <xs:element name="city" type="xs:string"/>
        <xs:element name="country" type="xs:string"/>
      </xs:sequence>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>