Difference between IEEE address and extended address

hi,

I am confused between IEEE address and extended address.  I read in some document that by default extended address is the IEEE address. but some other document says that in order to associate all the devices ' to a particular network ' we use extended address  ( i.e., match the extended address for joining ).

Can any one explain me what are these addresses? are they same? if not, whats the difference and where to use them.

Thanks in advance.

Mahesh kv