Echoes
Echoes
What Stays Behind
In 1987, a conservation scientist soaked treated ceramics in solvent for eight hours. Roughly half the resin stayed behind. The treatment was considered reversible. Barbara Appelbaum argued that her profession needed a better question than whether something could be undone, and proposed asking instead what any intervention leaves available to whoever has to work on the object next. Nearly four decades later, the W3C is working out when software agents should be allowed to commit users to transactions they cannot fully reverse — arriving at the same problem, apparently without knowing it had already been formalized.
What Stays Behind
In 1987, a conservation scientist soaked treated ceramics in solvent for eight hours. Roughly half the resin stayed behind. The treatment was considered reversible. Barbara Appelbaum argued that her profession needed a better question than whether something could be undone, and proposed asking instead what any intervention leaves available to whoever has to work on the object next. Nearly four decades later, the W3C is working out when software agents should be allowed to commit users to transactions they cannot fully reverse — arriving at the same problem, apparently without knowing it had already been formalized.
Atomicity Sidebar
Inside a single database, rolling back a transaction is erasure. The writes vanish, the locks release, the data looks exactly as if you'd never tried. Jim Gray described this in 1981: a transaction transforms state atomically, or it doesn't. Härder and Reuter named the properties ACID in 1983, and for a generation of engineers, "rollback" meant the system handled it.
Then systems outgrew a single machine. Two-phase commit tried to extend the boundary across nodes, but it introduced a blocking problem that turned out to be mathematically inherent — if a participant crashes mid-vote, everyone waits. Garcia-Molina and Salem's 1987 Saga paper proposed the pragmatic fix: break a long transaction into steps that each commit immediately, and if something fails partway through, run compensating transactions in reverse order.
But compensation isn't erasure. It's a new event. The hotel reservation gets canceled, not unbooked. The charge gets refunded, not erased from the ledger. The world saw the intermediate states and kept moving. When modern workflow engines apply sagas across payment rails, third-party APIs, and human approvals, each "rollback" is really a fresh transaction whose business effect is intended to offset the first. Whether it actually does depends on timing, on the external service accepting it, and sometimes on someone picking up the phone.
Fifty Percent Still There — A Museum Conservator Looks Inside the Undo Button
CONTINUE READINGNever Erase
The Ledger That Never Forgets
In 1494, a Franciscan friar wrote down what to do when you post the wrong number: don't erase it. Add a second entry explaining the mistake, then record the correction. Three entries where one scratch-out would do. Venetian merchants had already settled on the slower method, and eventually federal law agreed with them. The wrong entry still belongs in the book. Any system that overwrites what was there before faces the question they answered.
The Chart That Cannot Be Unwritten
A chiropractor recopied a patient's chart after a malpractice complaint arrived. The rewritten version described a patient who had improved and was satisfied. The original, which the patient happened to have copied, described neither. Healthcare learned case by case, and expensively, that altering a clinical record does more than revise the past. It cuts the reasoning out from under decisions other people already made on the strength of it.
Further Reading
