Design Patterns when you want to keep history of changes
After having the problem of keeping history of about everything, someone told me to look at Martin Fowler's website (who works for ThoughtWorks. The current article Patterns for things that change with time demonstrate some way of beeing able to know how a database entity was at a fixed point of time. Audit Log, Effectivity, Temporal Property, Snapshot, Temporal Objects and Timepoint are some patterns that are know functionnal.
-f.