Advanced query rewrite

Hi!

I was looking into the PostgreSQL RULE system in order to define rewriting /
redirecting queries under certain conditions. For my part I would like to
fully be able to control the query rewrite, e.g by implemening a stored
procedure to define the query rewrite results, since as it seems the means
of defining a SELECT RULE doesn't fullfill my requirements. Does anyone
know if that would be possible?

What I wan't to achieve is to implement a "agggregare (summary table)
navigator" which should transparently rewrite SQL directed to certain large
tables to related summary tables instead and for this the RULE system seems
too limited (without being able to implement an own rewrite procedure).

Any input on this matter would be much appreciated!

Thanks and Regards,
Christian