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

    <xs:complexType name="PublicationType">
        <xs:sequence>
            <xs:element name="Title" type="xs:string"/>
            <xs:element name="Author" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element name="Date" type="xs:gYear"/>
        </xs:sequence> 
    </xs:complexType>
    
    <xs:complexType name="BookType">
        <xs:complexContent>
            <xs:extension base="PublicationType" >
                <xs:sequence>
                    <xs:element name="ISBN" type="xs:string"/>
                    <xs:element name="Publisher" type="xs:string"/>
                </xs:sequence>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>
        
    <xs:complexType name="MagazineType">
        <xs:complexContent>
            <xs:restriction base="PublicationType">
                <xs:sequence>
                    <xs:element name="Title" type="xs:string"/>
                    <xs:element name="Date" type="xs:gYear"/>
                </xs:sequence>
            </xs:restriction>
        </xs:complexContent>
    </xs:complexType>
    
</xs:schema>
