An AT URI is DID, collection and record key; collections are reversed-domain NSIDs; most keys are TIDs that sort by time; some collections hold one record keyed self; resolution goes through the DID to the host.

Addresses that survive a change of host are what portability needs.

A record's address is an AT URI: a street address with three parts. The DID. Then the collection. Then the record key.

The collection is a name with a domain in it, reversed. app dot bsky dot feed dot post. The domain says who defined it.

Most record keys are TIDs: thirteen characters made from a timestamp. They sort by time.

Some collections hold one record, keyed self. Your profile is one.

Resolve the DID to find the host. Ask the host for the collection and key. The address works no matter which server holds the data.

Terms. NSID: namespaced identifier, the reversed-domain name of a collection or method. TID: timestamp identifier, the 13 character record key.

Check yourself. Which part of an AT URI says who defined the record type?