The Ledger and Immutable Database
A ledger database records data as an append only sequence of changes that, once written, cannot be edited or deleted. This fits finance, audit trails, and supply chains, where you must prove that history was not tampered with.
Append only history
In an ordinary table an update overwrites the old value, erasing the past. A ledger instead keeps every version as a new entry, so the full history of each record remains. You can ask what a value was at any past moment, which is called time travel.
Cryptographic verification
To prove integrity, each entry is hashed, and that hash includes the hash of the previous entry, forming a chain. Any change to an old entry would change its hash and break every later link, so tampering is detectable.
- The chain of hashes is like a sealed audit log.
- A verification check recomputes hashes to confirm nothing changed.
- This is the same idea that underlies blockchains, without needing many parties.
Key idea
A ledger database keeps an append only, hash chained history so every past value is preserved and any later alteration is provably detectable.