Oracle Message OCI-30938 - No prefix defined for namespace string (particle string)

ERROR	No prefix defined for namespace string (particle string)
CAUSE	An XML namespace mapping (xmlns: =) must be defined for each particle (element or attribute) stored in an schema-constrained XMLType document.
ACTION	Add an xmlns attribute definition (attribute name=xmlns: prefix and value=namespace URL) to the current XMLType document. The safest place to add this attribute is in the root node of the document to ensure that the mapping will be in scope.