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

<xs:element name="catalog">
<xs:complexType>
<xs:sequence>
<xs:element ref="magazine" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="title" type="xs:string"/>
<xs:attribute name="publisher"  type="xs:string"/>
</xs:complexType>
</xs:element>


<xs:element name="magazine">
<xs:complexType>
<xs:sequence>
<xs:element ref="article" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="date" type="xs:string"/>
</xs:complexType>
</xs:element>

<xs:element name="article">
<xs:complexType>
<xs:sequence>
<xs:element name="title" type="xs:string"/>
<xs:element ref="author" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>

<xs:element name="author">
<xs:complexType>
<xs:sequence>
<xs:element name="firstname" type="xs:string"/>
<xs:element name="lastname" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>

</xs:schema>