How to query and extract a specific XML tag value from Oracle CLOB field containing XML data

I have an Oracle table with a CLOB field that contains XML-Data. I would like query this table and make use of Oracles xmltype function and extract the value of a specific XML-Tag.
Oracle returns me all subelements of the root node. When I try to extract values of nodes further down in the xml-tree hierarchy I get no result.

I would be grateful if you could help me.

Best regards,
Wil


Table definition:
CREATE TABLE user.XML_TABLE
(
  XML_DATA                CLOB
)


Example clob field contents (field xml_data):

<xml-fragment client="muster_max" offerId="0000900513000000" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">

  <product productId="PROD-ID" code="AB-CD" type="TYPE_X" xmlns="http://www.something.com/is/xml/offer">Product Name</product>

      .... further tags ...

</xml-fragment>



Queries:
1) select xmltype(xml_data) from XML_TABLE;
select extract(xmltype(xml_data),'/xml-fragment') from XML_TABLE;

Both queries return the whole contents of the field xml_data

2) select extract(xmltype(xml_data),'/xml-fragment/*') from XML_TABLE
The query returns all subelements of tag <xml-fragment></xml-fragment>

3) select extract(xmltype(xml_data),'/xml-fragment/product/*') from XML_TABLE
The query returns nothing. I would expect to receive all subelements of node product.

4) select extract(xmltype(xml_data),'/xml-fragment/product/text()') from XML_TABLE
The query returns nothing. I would expect to receive the value 'Product name'