<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:complexType name="article_type">
        <xs:sequence>
            <xs:element name="title" type="xs:string"/>
            <xs:element name="author">
                <xs:complexType>
                    <xs:simpleContent>
                        <xs:extension base="xs:string">
                            <xs:attribute name="degree" type="xs:string"/>
                            <xs:attribute name="gender">
                                <xs:simpleType>
                                    <xs:restriction base="xs:string">
                                        <xs:enumeration value="male"/>
                                        <xs:enumeration value="female"/>
                                    </xs:restriction>
                                </xs:simpleType>
                            </xs:attribute>
                        </xs:extension>
                    </xs:simpleContent>
                </xs:complexType>
            </xs:element>
        </xs:sequence>
        <xs:attribute name="date" type="xs:string"/>
        <xs:attribute name="level" type="xs:string"/>
    </xs:complexType>
    <xs:element name="article" type="article_type"/>
    <xs:complexType name="journal_type">
        <xs:sequence>
            <xs:element ref="article" minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="title" type="xs:string"/>
        <xs:attribute name="publisher" type="xs:string"/>
    </xs:complexType>
    <xs:element name="journal" type="journal_type"/>
    <xs:complexType name="catalog_type">
        <xs:sequence>
            <xs:element ref="journal" minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
    </xs:complexType>
    <xs:element name="catalog" type="catalog_type"/>
</xs:schema>
