Immutable Data

Immutable data is data that, once recorded, is never edited or overwritten; any correction adds a new record rather than changing the old one.

Immutability in event-based analytics is a deliberate architectural choice, not a limitation: an event is a historical fact — “the user did this at that moment” — and a past fact should not change. Its benefit is that history stays trustworthy and the past can be reconstructed as it was; this is why immutable data underpins any audit and any reliable trend report. But its cost must also be seen: if data is recorded wrong, it cannot be erased but must sit beside a corrective record, and this is in tension with the “right to be forgotten,” because fully deleting one person's data in a system that erases nothing is harder. Good immutability means the event stays untouched yet a path still exists to legally delete personal data.