using window-functions to get freshest value - how?

["Massa, Harald Armin" <chef@xxxxxxx>]

I have a table

CREATE TABLE rfmitzeit
(
  id_rf inet NOT NULL,
  id_bf integer,
  wert text,
  letztespeicherung timestamp without time zone
  CONSTRAINT repofeld_id_rf PRIMARY KEY (id_rf),
  );
  
  
where for one id_bf there are stored mutliple values ("wert") at multiple dates:
    
    id_bf,  wert, letztespeicherung:
    98,  'blue', 2009-11-09
    98,  'red', 2009-11-10
    
    
now I have a select to get the "youngest value" for every id_bf:
    
select
	rfmitzeit.id_bf, rfmitzeit.wert
    from
	rfmitzeit
	join
	(select
	    id_bf, max(rfmitzeit.letztespeicherung) as maxsi
	 from
	    rfmitzeit 
	group by id_bf
	) idbfzeit on (rfmitzeit.id_bf=idbfzeit.id_bf and rfmitzeit.letztespeicherung=idbfzeit.maxsi)  

which works quite fine. But I want to extend my knowledge.... 

so I have the feeling that this should be possible using a WINDOW-function, 
but I can not find out how. (besides curiousity, I also want to test if doing this kind of query with window-functions will be faster)

Is it possible? How would the SQL utilizing WINDOW-functions look like?

Best wishes,

Harald

-- 
GHUM Harald Massa
persuadere et programmare
Harald Armin Massa
Spielberger Straße 49
70435 Stuttgart
0173/9409607
no fx, no carrier pigeon 
-
%s is too gigantic of an industry to bend to the whims of reality