xml : Optional and Required Attributes

Attributes are optional by default. You can specify required attributes using “use” attribute of element tag.

Example

<xs:element name=”type” type=”xs:string” use=”required” />

<xs:element name="address">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="city" type="xs:string" />
      <xs:element name="district" type="xs:string" />
      <xs:element name="state" type="xs:string" />
      <xs:element name="country" type="xs:string" />
    </xs:sequence>
    <xs:attribute name="type" type="xs:string" use="required" />
    <xs:attribute name="from" type="xs:date" />
  </xs:complexType>
</xs:element>

Above code snippet specifies “type” for the element “address” is a required attribute.

student.xsd

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="student">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="firstname" type="xs:string" />
                <xs:element name="middlename" type="xs:string" />
                <xs:element name="lastname" type="xs:string" />
                <xs:element name="age" type="xs:integer" />
                <xs:element name="department" type="xs:string" default="CSE" />
                <xs:element name="dresscode" type="xs:string" fixed="Black and White" />
                <xs:element name="address">
                    <xs:complexType>
                        <xs:sequence>
                            <xs:element name="city" type="xs:string" />
                            <xs:element name="district" type="xs:string" />
                            <xs:element name="state" type="xs:string" />
                            <xs:element name="country" type="xs:string" />
                        </xs:sequence>
                        <xs:attribute name="type" type="xs:string" use="required" />
                        <xs:attribute name="from" type="xs:date" />
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

student.xml

<?xml version="1.0" encoding="UTF-8"?>

<student xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="student.xsd">
    <firstname>hari</firstname>
    <middlename>krishna</middlename>
    <lastname>gurram</lastname>
    <age>25</age>
    <department></department>
    <dresscode>Black and White</dresscode>
    <address from="1989-05-06">
        <city>Ongole</city>
        <district>Prakasam</district>
        <state>Andhra Pradesh</state>
        <country>India</country>
    </address>
</student>

Above xml file doesn’t specifies the type attribute for address element. So when you tries to validate you will get below error.

XML validation started.

Checking file:student.xml...

Referenced entity at "file:student.xsd".

cvc-complex-type.4: Attribute 'type' must appear on element 'address'. [11]

XML validation finished.

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