Insert into XML TYPE table in Oracle

I am trying to repeat the samples in this post, but run into some errors:
http://www.oracle.com/technology/pub/articles/quinlan-xml.html
I have 0 knowledge about XML and Oracle XMLDB
If you would like to repeat,  please note that xsd file needs being revised:
1.  change xmlns:xdb=http://xmlns.oracle.com/xdb    to
                  xmlns:xdb="http://xmlns.oracle.com/xdb"
2.  Add line </xs:complexType> right after <xs:attribute name="id" type="xs:string" use="required"/>.  
Before I made the changes,  I could not register the schema.  (I knows nothing about XML,  but somehow figured out that "bug" :-).
After I register the schema,  I tried to do the insert and erroed out
(See the last step in the Code section).
I copied the two txt and the xsd files here.  All 3 files are stored in /tmp directory.
Could some Oracle XMLDB or XML expert out here shed me some light what I
missing and how I can insert into the table after I register the schema?
I really appreciate it.  Thx  If you could,  please email your response to me:
musicbeginner@yahoo.com
Sean
=======================================================

invoicexml.txt file:
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:xdb="http://xmlns.oracle.com/xdb" version="1.0">
<xs:element name="INVOICESCHEMA" xdb:defaultTable="INVOICESCHEMA">
   <xs:complexType>
        <xs:sequence>
             <xs:element name="MailAddressTo">
                   <xs:complexType>
                         <xs:sequence>
                              <xs:element name="Person" type="xs:string"/>
                              <xs:element name="Street" type="xs:string"/>
                         </xs:sequence>
                       <xs:attribute name="id" type="xs:string" use="required"/>
                   </xs:complexType>
             </xs:element>
        </xs:sequence>
  </xs:complexType>
</xs:element>
</xs:schema>

===============
invoiceformtest.xsd  and invoiceformtest.txt files:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:xdb="http://xmlns.oracle.com/xdb" version="1.0">
<xs:element name="INVOICEFORMTEST" xdb:defaultTable="INVOICEFORMTEST">
   <xs:complexType>
      <xs:sequence>
         <xs:element name="MailAddressTo">
            <xs:complexType>
               <xs:sequence>
                  <xs:element name="Person" type="xs:string"/>
                  <xs:element name="Street" type="xs:string"/>
                  <xs:element name="City" type="xs:string"/>
                  <xs:element name="State" type="xs:string"/>
                  <xs:element name="Zipcode" type="xs:string"/>
               </xs:sequence>
               <xs:attribute name="id" type="xs:string" use="required"/>
            </xs:complexType>
         </xs:element>
      </xs:sequence>
   </xs:complexType>
</xs:element>
</xs:schema>

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Here are the code I used try to repeat the samples:
 
create directory XMLDIR as '/tmp';    
 
create table invoiceXML_col (
inv_id number primary key,
inv_doc XMLType);
 
-- create table invoiceXML_tbl of XMLtype;
 
Insert into invoicexml_col values (1,
XMLType(bfilename('XMLDIR', 'invoicexml.txt'),
nls_charset_id('AL32UTF8') ));
 
Insert into invoicexml_tbl values
(XMLType(bfilename('XMLDIR', 'invoicexml.txt'),
 nls_charset_id('AL32UTF8')));
-- register schema
BEGIN
    DBMS_XMLSCHEMA.registerSchema(
        SCHEMAURL => 'http://xmlns.oracle.com/xdb/invoiceformtest.xsd',
        SCHEMADOC => bfilename('XMLDIR','invoiceformtest.xsd'),
        CSID => nls_charset_id('AL32UTF8'));
   END;
/
Insert into invoiceformtest values
(XMLType(bfilename('XMLDIR', 'invoiceformtest.txt'), nls_charset_id('AL32UTF8')
        )
);
 
ERROR at line 1:
ORA-30937: No schema definition for 'schema' (namespace 'http://www.w3.org/2001/XMLSchema') in parent '/'