...
	<xs:complexType name="Contract">
		<xs:annotation>
			<xs:documentation>Договор</xs:documentation>
		</xs:annotation>
		<xs:sequence>
			<xs:choice>
				<xs:element minOccurs="1" name="Owner" type="Person">
					<xs:annotation>
						<xs:documentation>физическое лицо</xs:documentation>
					</xs:annotation>
				</xs:element>
				<xs:element name="OwnerJuridical" type="JuridicalPerson">
					<xs:annotation>
						<xs:documentation>юридическое лицо</xs:documentation>
					</xs:annotation>
				</xs:element>
			</xs:choice>
...      
		</xs:sequence>
	</xs:complexType>
...

    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "4.0.0.0")]
    [System.ServiceModel.MessageContractAttribute(WrapperName="AddContract", WrapperNamespace="что-то_там", IsWrapped=true)]
    public partial class AddContractRequest {
        
        [System.ServiceModel.MessageBodyMemberAttribute(Namespace="", Order=0)]
        [System.Xml.Serialization.XmlElementAttribute(" Owner", typeof(Person), Form=System.Xml.Schema.XmlSchemaForm.Unqualified)]
        [System.Xml.Serialization.XmlElementAttribute(" OwnerJuridical", typeof(JuridicalPerson), Form=System.Xml.Schema.XmlSchemaForm.Unqualified)]
        public object Item;
    ...