using window-functions to get freshest value - how?

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
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