Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://example.com/books"
    xmlns:bk="http://example.com/books"
    elementFormDefault="qualified">

<xs:element name="library" type="bk:LibraryType"/>

<xs:complexType name="LibraryType">
        <xs:sequence>
            <xs:element name="book" type="bk:BookType"
                        minOccurs="1" maxOccurs="unbounded"/>
        </xs:sequence>
    </xs:complexType>

<xs:complexType name="BookType">
        <xs:sequence>
            <xs:element name="title"  type="xs:string"/>
            <xs:element name="author" type="xs:string"
                        minOccurs="1" maxOccurs="unbounded"/>
            <xs:element name="year"   type="xs:gYear"/>
            <xs:element name="price"  type="bk:PriceType"
                        minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="id"       type="xs:ID"      use="required"/>
        <xs:attribute name="category" type="bk:CategoryEnum" use="required"/>
    </xs:complexType>

<xs:simpleType name="CategoryEnum">
        <xs:restriction base="xs:string">
            <xs:enumeration value="fiction"/>
            <xs:enumeration value="non-fiction"/>
            <xs:enumeration value="reference"/>
        </xs:restriction>
    </xs:simpleType>

<xs:complexType name="PriceType">
        <xs:simpleContent>
            <xs:extension base="xs:decimal">
                <xs:attribute name="currency" type="xs:string" use="required"/>
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>

</xs:schema>