with tmp as
 (select '<?xml version="1.0" encoding="UTF-8"?>
<item xmlns:ns1="http://abcd.ejb.app.aaa.bb.ru" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="ns1:itemBIG">
   <mainId>152545</mainId>
   <id2>
      <id3>6789</id3>
   </id2>
   <id4>03</id4>
</item><record>
   <Id>XD123</Id>
</record><Date>2019-01-02</Date>' sXML  from dual)

select t.*
  from tmp,
       XMLTable(xmlnamespaces('http://abcd.ejb.app.aaa.bb.ru' as "ns1",
                              'http://www.w3.org/2001/XMLSchema-instance' as "xsi",
                              'ns1:itemBIG' as "type"),
                '/record' passing XMLType(sXML) 
                columns 
                recordID  varchar2(40) path 'Id') t;

with tmp as
 (select '<?xml version="1.0" encoding="UTF-8"?>
<item xmlns:ns1="http://abcd.ejb.app.aaa.bb.ru" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="ns1:itemBIG">
   <mainId>152545</mainId>
   <id2>
      <id3>6789</id3>
   </id2>
   <id4>03</id4>
</item><record>
   <Id>XD123</Id>
</record><Date>2019-01-02</Date>' sXML  from dual)

select t.*
  from tmp ,
       XMLTable(xmlnamespaces('http://abcd.ejb.app.aaa.bb.ru' as "ns1",
                              'http://www.w3.org/2001/XMLSchema-instance' as "xsi",
                              'ns1:itemBIG' as "type"),
                '/ns1:itemBIG' passing XMLType(replace(replace(sXML, '<item', '<ns1:itemBIG'), 'itemBIG">', 'itemBIG"><item>')||'</ns1:itemBIG>') 
                columns 
                recordID  varchar2(40) path 'record/Id') t;