It looks like Preserves just uses version numbers in its schemas. On the other hand, you can read the data without a schema, similar to JSON.
The schema language is extensible/evolvable in that pattern matching ignores extra entries in a sequence and extra key/value pairs in a dictionary. So you could have a "version 1" of a schema with
Person = <person @name String> .
Person = @v2 <person @name String @address Address>
/ @v1 <person @name String> .
The schema language is in production but the design is still a work in progress and I expect more changes before a 1.0 release of the schema language.
(The schema language is completely separate from the preserves data model, by the way -- one could imagine other schema languages being used instead/as well)
Protobufs have an extra level of indirection built in: code refers to fields using names, but numbers are sent on the wire. Without convenient access to field numbers, they can’t as easily be hard-coded. This also strongly encourages using the schema file for most tasks. With protobufs (or similar), any user-friendly editor will need a schema to make sense of the data.
JSON-like systems and protobufs have opposite design goals: encouraging versus discouraging schemaless data access.
Person = <person @name String @address Address>
Person = <person {
@name "name": String
@address "address": Address
}>
Person = {
@name 1: String
@address 2: Address
}
export type Person = {
name: String,
address: Address,
};