GROGGS was a university bulletin board system which existed between 1986 and 2020. I am in the process of building its replacement. The threading format is in a style I haven’t seen elsewhere, so I am considering ideas about how to federate it. I am posting here in case other people have suggestions.

The discussion space is flat rather than threaded: it consists of items, which have subjects, and replies to those items. However, there is a limit to the size of an item. When a user attempts to reply to an item which is full, they are asked for a new subject line; then, a “continuation” item is created which is threaded back to the previous one. This slows thread drift. The index shows the subject line of the most recent continuation.

(Versions later than the mid-1990s had a standard TCP protocol, which may shine a different light on the problem space.)

I see three problems with adapting the usual use of ActivityPub, as used e.g. by Mastodon.

Firstly, the fact that items are flat-file rather than threaded. This must have been handled before by other projects, no? I think it can be dealt with by editing the reply-to of the received replies before they appear in the outbox.

Secondly, the subject lines. Mastodon uses the “subject” field for content warnings, which may become a nuisance for interoperativity.

Thirdly, the change of subject line when a continuation begins, assuming we’re not using the “subject” field. My thinking is that a system message will be inserted after the last message of a full item, saying “This item is full and if you reply to it you will start a continuation”. Then the first line of the reply text can be taken as the new subject line.

But if we are using the “subject” field, we need to be able to address the requirement that the subject line changes when you begin a continuation-- rejecting messages which have the same subject line as the current item, with a private message, I suppose.

Thoughts?