Aruna,
xmlns is an attribute which points to the namespaces of prefixes used in an xml document. It helps the XML parsers to lookup to the acutal location of the XML document which the prefix refers to.
targetNameSpace is used to allocate the XML document to any location outside the default namespace(
http://www.w3.org/2001/XMLSchema)
Let me know if this helps.
Thanks,
Anila