Hello Ppl...well i have a big problem doing this query....

i need to convert the below query into relational algebra statements...and OPTIMIZE IT as well cud u pls help me out here....

The query to be converted is ...

select Raddress, O.R#, O.Model#
from Excess E, Orders O, Retail R
where R.R#=O.R# AND O.Date=(E.Date+7) AND E.Qty>10 AND O.Qty>20 AND E.R#=O.R# AND E.Model#=O.Model#

The description of the above mentioned tables is as follows

Excess (R#, Model#, Quantity, Date)
Orders (R#, Model#, Quantity, Date)
Retail (R#, Raddress, Phone#)

Im having some problems to convert this above query into relational algebra...so pls help me out here....

thanks