problem with occurence of elements

Hello schema-users,

I have as I hope a very simple problem. Unfortunately not for me:

This is my complexType:

    <xs:complexType name="chapterType">
        <xs:sequence>
            <xs:element name="title"/>
                <xs:choice>
                    <xs:element name="subtitle"/>
                    <xs:element name="author"/>
                    <xs:element name="para"/>
                    <xs:element name="sect1"/>
                </xs:choice>
        </xs:sequence>
    </xs:complexType>

I try to realise, that after the required title-element the author-, 
para- and sect1-element can occure unboundedly and the subtitle-element 
can occure only once. There should also be the restriction that if an 
sect1-element occures the para-, author- or subtitle-element should not 
occure.

Is this possible using schema? I would be very thankful for every hint 
solving my problem.

Andreas