<xsd:schema
    xmlns:xsd="http://www.w3.org/2000/10/XMLSchema"
    >

    <xsd:element name="authors" type="authorsType" />
    <xsd:complexType name="authorsType">
        <xsd:sequence>
            <xsd:element ref="author"/>
            <xsd:choice maxOccurs="unbounded" minOccurs="0">
                <xsd:element ref="author"/>
                <xsd:element name="cooperation" type="xsd:string"/>
            </xsd:choice>
        </xsd:sequence>
    </xsd:complexType>

    <xsd:complexType name="author">
        <xsd:sequence>
            <xsd:element name="description" type="xsd:string"/>
        </xsd:sequence>
    </xsd:complexType>

</xsd:schema>
