variable date precision

hi there

i've got a problem with a field set up as type date.  now we discovered that we have to allow not only full dates
(2003-10-16)but also dates where we have only a month or even a year.  we see that it is not a very good practice to
usethe first of the month because it is ambiguous. on the other side, date does not allow entries like "2003-10-00". 

this db already contains quite a few records, so i'm not really keen on changing the data-type.  nevertheless, i'm
interestedin the theoretically correct solution as much as in a practical one, since it is not the first time i've come
acrossthis problem. 

any suggestions are very welcome...

chris