with t
    as
    (
     select '<EffeCTIveDate>01/01/2015</effeCTiveDate>' str from dual
     union all
     select '<description>TESTING xml</DescripTion>' str from dual
     union all
     SELECT '<projectNumber>311879</projectNumber>' from dual
     UNION ALL
     SELECT '<Test/>' FROM DUAL
    )
select lower(regexp_substr(regexp_substr(str,'[^<]+',1,1),'[^/>]+',1,1)) FROM t ;

select xmltype('<base>
                   <tag1>1</tag1>
                   <tag2>2</Tag2>
                </base>')
from dual;

ORA-31011: XML parsing failed
ORA-19202: Error occurred in XML processing
LPX-00225: end-element tag "Tag2" does not match start-element tag "tag2"
Error at line 3
ORA-06512: at "SYS.XMLTYPE", line 310
ORA-06512: at line 1
31011. 00000 -  "XML parsing failed"
*Cause:    XML parser returned an error while trying to parse the document.
*Action:   Check if the document to be parsed is valid.

CREATE TABLE xmldata
(
 xid NUMBER,
 xname VARCHAR2(20),
 xdata CLOB
 );

 INSERT INTO xmldata
 values (1,'Parse xml', '<?xml version="1.0"?>
<company>
        <Employee>
                <FirstName>Tom</firstname>
                <LastName>Cruise</LASTNAME>
        </Employee>
        <employee>
                <FirstName>Paul</FIRSTNAME>
                <LastName>Enderson</lastname>
        </employee>
        <Employee>
                <FirstName>George</firstname>
                <LastName>Bush</lastname>
        </EmployEE>
</company>');

SQL> with
  2    data as (select
  3  '<?xml version="1.0"?>
  4  <company>
  5          <Employee>
  6                  <FirstName>Tom</firstname>
  7                  <LastName>Cruise</LASTNAME>
  8          </Employee>
  9          <employee>
 10                  <FirstName>Paul</FIRSTNAME>
 11                  <LastName>Enderson</lastname>
 12          </employee>
 13          <Employee>
 14                  <FirstName>George</firstname>
 15                  <LastName>Bush</lastname>
 16          </EmployEE>
 17  </company>' val from dual
 18    ),
 19    tags as (
 20      select regexp_substr(val,'<[^>]+>',1,column_value) tag
 21      from data,
 22           table(cast(multiset(select level from dual
 23                               connect by level <= regexp_count(val,'<')+1)
 24                 as sys.odciNumberList))
 25    )
 26  select distinct rtrim(ltrim(lower(tag),'</'),'>') tag
 27  from tags
 28  where tag is not null and tag not like '<?%'
 29  /
TAG
------------------------------------------------------------------------------
company
firstname
employee
lastname

4 rows selected.