Maybe i misunderstood what you looking for but here goes anyway.....
I always treat regression testing as basically what system/software did in the past. This however isn't totally the solution as i'm sure software may have done things in the last version/release that were not necessary or required.
Like all forms of testing its probably dependent greatly on proper updating of test specs docs from the requirements?
As we continue to try to implement automated testing here i'll be trying to make regression tests as its primary aim.