Fable
The waterwheel sends every village's ledger into the same mill
The three mills in the valley each recorded grain prices, inventory, and credit separately, but the chamber of commerce wanted to view them together every day. When people were sent temporarily to copy the ledgers, units, times, and missing fields were always inconsistent, and a late page could cause the general ledger to misjudge.
The bridge repairer installed an account-taking port on each mill: first authenticate the visitor, then take incremental accounts in the agreed format, preserving source, time, and weight units. When there is a bad account or a broken bridge, the entrance clearly returns an error and does not write guesses into the general ledger.
The guild also found that some warehouse ledgers were only allowed to be viewed by their own workshop. So the ledger-fetching gateway carried permission tags along, synced only newly added or changed records, and left a trace of who read them and when.
A rainstorm damaged the waterwheel, and the bridge repairer continued from the last successful position instead of copying all three mills from the beginning. Retries, rate limiting, and handling of duplicate records were all written into the rules.
A connector is therefore not a one-time migration script, but the boundary responsible for authentication, transformation, synchronization, and traceability when external systems enter AI retrieval and workflows.