XML/XML Schema/default

default value is one of the value in restriction

File: Data.xml
<?xml version="1.0"?>
<images xmlns="http://www.wbex.ru"
                   xmlns:i="http://www.wbex.ru"
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                   xsi:schemaLocation= "http://www.wbex.ru Schema.xsd">
    <image/>                                                  
    <image i:src="http://www.wbex.ru/style/logo.png"/> 
</images>
File: Schema.xml
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            targetNamespace="http://www.wbex.ru"
            xmlns="http://www.wbex.ru"
            elementFormDefault="qualified">
    <xsd:element name="image">
        <xsd:complexType>
            <xsd:attribute ref="src" default="http://www.wbex.ru"/>
        </xsd:complexType>
    </xsd:element>
    <xsd:attribute name="src">
        <xsd:simpleType>
            <xsd:restriction base="xsd:anyURI">
                <xsd:enumeration value="http://www.wbex.ru"/>
                <xsd:enumeration value="http://www.wbex.ru/style/logo.png"/>
                <xsd:enumeration value="http://www.wbex.ru/isbn.html"/>
            </xsd:restriction>
        </xsd:simpleType>
    </xsd:attribute>
    <xsd:element name="images">
        <xsd:complexType>
            <xsd:sequence>
                <xsd:element ref="image" maxOccurs="2"/>
            </xsd:sequence>
        </xsd:complexType>
    </xsd:element>
</xsd:schema>

Element with default value

File: Data.xml
<?xml version="1.0"?>
<airport xmlns="http://www.wbex.ru"
                   xmlns:ex="http://www.wbex.ru"
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                   xsi:schemaLocation= "http://www.wbex.ru Schema.xsd">
    <aircraft/>
    <aircraft>F-16</aircraft>
</airport>
File: Schema.xsd
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            targetNamespace="http://www.wbex.ru"
            xmlns="http://www.wbex.ru"
            elementFormDefault="qualified">
    <xsd:element name="airport">
        <xsd:complexType>
            <xsd:sequence>
                <xsd:element name="aircraft" default="Boeing 747"  maxOccurs="2" type="xsd:string"/>
            </xsd:sequence>
        </xsd:complexType>
    </xsd:element>
</xsd:schema>