When elements are not nested, no implicit relations are created. You can, however, explicitly specify relations between elements that are not nested using the msdata:Relationship annotation.
The following example shows an XML Schema in which the msdata:Relationship annotation is specified between the Order and OrderDetail elements, which are not nested. The msdata:Relationship is specified as the child element of the Schema element.
<xs:schema id="MyDataSet"  
             xmlns:xs="http://www.w3.org/2001/XMLSchema" 
             xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
 <xs:element name="MyDataSet" msdata:IsDataSet="true">
  <xs:complexType>
    <xs:choice maxOccurs="unbounded">
      <xs:element name="OrderDetail">
       <xs:complexType>
         <xs:sequence>
           <xs:element name="OrderNo" type="xs:string" />
           <xs:element name="ItemNo" type="xs:string" />
         </xs:sequence>
       </xs:complexType>
      </xs:element>
      <xs:element name="Order">
       <xs:complexType>
         <xs:sequence>
           <xs:element name="OrderNumber" type="xs:string" />
           <xs:element name="EmpNumber" type="xs:string" />
         </xs:sequence>
       </xs:complexType>
      </xs:element>
    </xs:choice>
  </xs:complexType>
  </xs:element>
   <xs:annotation>
     <xs:appinfo>
       <msdata:Relationship name="OrdOrdDetailRelation"
                            msdata:parent="Order" 
                            msdata:child="OrderDetail" 
                            msdata:parentkey="OrderNumber" 
                            msdata:childkey="OrderNo"/>
     </xs:appinfo>
  </xs:annotation>
</xs:schema>
The XML Schema definition language (XSD) schema mapping process creates a DataSet with Order and OrderDetail tables and a relationship specified between these two tables.
RelationName: OrdOrderDetailRelation
ParentTable: Order
ParentColumns: OrderNumber 
ChildTable: OrderDetail
ChildColumns: OrderNo 
Nested: False
See Also
Generating DataSet Relations from XML Schema (XSD) | Mapping XML Schema (XSD) Constraints to DataSet Constraints | Data Type Support between XML Schema (XSD) Types and .NET Framework Types