Excision

Datomic is a kind of neat database that I haven't really looked into. The upshot is that it tracks changes in data over time; when a fact is added, it remembers when it was added, so you can restore your state of knowledge at a given point in time.

There are requirements, though (e.g. privacy laws) that require information to be removed outright - that you forget you ever knew it in the first place - and this is excision.