How retreive Sum of values between 2 dates?

Add-ons Persistence Services
1

HI,
I use RRD4J and DB4O for some data and i need retreive Sum of values between 2 dates and Max/Min between 2 dates.
Available persistence extensions uses “Since”, and i don’t find anyway to calculate sum of values between 2 dates with those expressions… But i am not a specialist !
Somedoby has a solution or just a way for this?

Thanks

2

To find sumBetween(A,B), could you use sumSince(A) - sumSince(B)?