如何在XSD中限制元素的属性？

Question

I have this XML code:

 <student>
    <name sex="male">
        <fname></fname>
        <lname></lname>
    </name>
</student>

What I want to do is to add a restriction to the sex attribute. sex attribute should only take male and female as their value. I have basic knowledge of making this XML Schema. So far what I've done is this:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="name" type="nameType"/>
    <xs:element name="fname" type="xs:string"/>
    <xs:element name="lname" type="xs:string"/>
    <xs:element name="student" type="studentType"/>

    <xs:complexType name="nameType">
        <xs:sequence>
            <xs:element ref="fname"></xs:element>
            <xs:element ref="lname"></xs:element>
        </xs:sequence>
        <xs:attribute name="sex"></xs:attribute>
    </xs:complexType>

    <xs:complexType name="studentType">
        <xs:sequence>
            <xs:element ref="name"></xs:element>
        </xs:sequence>
    </xs:complexType>
</xs:schema>

Answer 1

You can add restriction to the value of the attribute as shown below:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="name" type="nameType"/>
    <xs:element name="fname" type="xs:string"/>
    <xs:element name="lname" type="xs:string"/>
    <xs:element name="student" type="studentType"/>

    <xs:complexType name="nameType">
        <xs:sequence>
            <xs:element ref="fname"></xs:element>
            <xs:element ref="lname"></xs:element>
        </xs:sequence>
        <xs:attribute name="sex">
            <xs:simpleType>
                <xs:restriction base="xs:string">
                    <xs:enumeration value="ar"></xs:enumeration>
                    <xs:enumeration value="en"></xs:enumeration>
                </xs:restriction>
            </xs:simpleType>
        </xs:attribute>
    </xs:complexType>

    <xs:complexType name="studentType">
        <xs:sequence>
            <xs:element ref="name"></xs:element>
        </xs:sequence>
    </xs:complexType>
</xs:schema>

Answer 2

Use xs:restriction to limit an attribute to a fixed set of enumerations via xs:enumeration :

<xs:attribute name="sex">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="male"/>
      <xs:enumeration value="female"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>

Two other observations:

1. You can shorten empty elements via <el/> notation.
2. In addition to allowing a student root element, your XSD would allow name , fname , and lname root elements. This doesn't look right. Perhaps you should define all or some of those locally rather than globally.

Here is your XSD with all of the above adjustments:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xs:element name="student" type="studentType"/>

  <xs:complexType name="studentType">
    <xs:sequence>
      <xs:element name="name" type="nameType"/>
    </xs:sequence>
  </xs:complexType>

  <xs:complexType name="nameType">
    <xs:sequence>
      <xs:element name="fname" type="xs:string"/>
      <xs:element name="lname" type="xs:string"/>
    </xs:sequence>
    <xs:attribute name="sex">
      <xs:simpleType>
        <xs:restriction base="xs:string">
          <xs:enumeration value="male"/>
          <xs:enumeration value="female"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:attribute>
  </xs:complexType>

</xs:schema>