Xml Schema creation - enforcing one tag at root

Question

I have a schema such as the one below but this permits any of the global element declarations to start as the root of an xml document.
I want just <table> to be at the root.
     <xs:element name="table">
          <xs:complexType>
               <xs:sequence>
                    <xs:element maxOccurs="unbounded" ref="tr"/>
               </xs:sequence>
               <xs:attributeGroup ref="attrs"/>
          </xs:complexType>
     </xs:element>
     <xs:element name="tr">
          <xs:complexType>
               <xs:sequence>
                    <xs:element maxOccurs="unbounded" ref="td"/>
               </xs:sequence>
               <xs:attributeGroup ref="attrs"/>
          </xs:complexType>
     </xs:element>
     <xs:element name="td">
          <xs:complexType mixed="true">
               <xs:complexContent>
                    <xs:extension base="Flow">
                         <xs:attributeGroup ref="attrs"/>
                         <xs:attributeGroup ref="cellvalign"/>
                    </xs:extension>
               </xs:complexContent>
          </xs:complexType>
     </xs:element>Must I have one global element to allow only one element as the document root?
i.e.
     <xs:element name="table">
          <xs:complexType>
               <xs:sequence>
                          <xs:element name="tr">
                             <xs:complexType ref="tr.c">
                    </xs:element >
               </xs:sequence>
            </xs:complexType>
      </xs:element>
     <xs:complexType name="tr.c">
          <xs:sequence>
               <xs:element maxOccurs="unbounded" ref="td"/>
          </xs:sequence>
          <xs:attributeGroup ref="attrs"/>
     </xs:complexType>
     thanks

Answer 1

I would rather use the flatter approach, the xhtml schema does how does it do it?
http://www.w3.org/2002/08/xhtml/xhtml1-transitional.xsd
Maybe I should explain more....
I wish to validate an xml document with a schema only, I pull the xml from within a propery file (Ugly I know). And keep it in memory.
The xml has no xsi attributes such as 'schemaLocation' , I tell the paser using a property the location of the external schema.
The outcome of validation is that the paser allows any globally declared element to be a root element when I wish just to have just one.
I guess the question is, what within the xml document or the schema tells the parser what the root element is?
cheers