recursive SQL

Hi

I have two tables:
Question              Response
----------              -----------
curr_id                 curr_id
prev_id                score

The question table holds a list of questions each with its own unique ID. The questions can change over time and when a change happens a new question is loaded into the question table with a new curr_id, The curr_id of the old question that the new one changed from is not removed from the table and to signify that the new question stemed from the old the old question Curr_id is placed into the new questions prev_id field.  The response table holds numeric responses to the questions.

Some possible values in these tables may be:

curr_id   prev_id         Qstn_id   Score
   1         -                           1         1
   2         1                      2         1
   3         -                           3         1
   4         -                           4         1
   5         3                           5         1
   6         -                           6         1
   7         5                           7         1


I want to find some SQL that will give a sum of all the scores for each question (excluding the old ones) that inclues the values of all previous versions of the question. So for example using the values above question 7 should receive a sumed up score of 3 (1 from id=7 1 from id=5 and 1 from id=3). I need to do this with straight SQL that can be used on multiple DBs. I've been struggling with this for a few days now with out any success. Does any one know how to do this or wether its possible.

Thanks
David