[str4d]

> But I’m still wondering how one would aggregate reactions. It seems it would not be enough just to have a PDS, but also to run an Indexer/Relay, which indexes other peoples PDS. And not just the PDSs of the people you are following, but also the rest of the world – after all a Like or such can come from everyone. When running an Indexer you are pretty soon into Firehose territory. Too much for a single person website.

You don't need to run a Relay yourself in order to see reactions; you instead subscribe to an existing Relay's firehose (such as the one that BlueSky PBC operates), and ignore anything that isn't "reaction-shaped" (matches the relevant Lexicon).

> Everyone talking about ATP seems to [..] never talk about the transmission mechanisms. Whereas I’m sitting here and thinking that an ActivityPub Actor’s Outbox is already a form of PDS – and it has an Inbox. Addressable via the Web and findable via Webfinger.

Here's my attempt to summarise the transmission difference between ActivityPub and AT Protocol: ActivityPub is symmetric and push-based, AT Protocol is asymmetric and pull-based.

With ActivityPub, your client talks to your server. The server handles both outgoing data (you making posts) and incoming data (viewing other people's posts).

When you create a post:

- The post is placed in your server's outbox.

- Your server looks up the servers for every one of your followers, and places your post in their inbox.

When someone creates a reaction:

- The reaction is placed in their server's outbox.

- Their server looks up your server, and places the reaction in its Inbox.

- Your website checks the Inbox, discovers the reaction, and handles it.

With AT Protocol, your client talks to your PDS and the client's App View. Your PDS handles outgoing data (you making posts), and your client's App View handles incoming data (viewing other people's posts). Relays are what provide transmission between the two: Relays subscribe to your PDS, and App Views subscribe to the firehose of at least on Relay.

When you create a post:

- The post is added to your repository on your PDS.

- The Relay pulls the post from your PDS and broadcasts it on its firehose.

- App Views see the post in the firehose, and include it within the feeds of users that follow you.

When someone creates a reaction:

- The reaction is added to their repository on their PDS.

- The Relay pulls the reaction from their PDS and broadcasts it on its firehose.

- Your website's App View (which might be your client's App View if "reactions" are also posts, or some other App View if this is a different kind of semantic data) sees the reaction in the firehose, and handles it (e.g. includes it within the feed of reactions that your website uses).

[ttepasse]

That is rather helpful, thanks!

But in a way depressing: I fear subscribing to a firehose is not that realistic for small single person websites. Maybe you can filter the firehose subscription.