On the other hand, however... If the ActivityPub API were used in an S2S context, enabling something like NodeBB to send activities on behalf of a Mastodon user, then it wouldn't matter that there is no GET /timeline, because all you need is POST /outbox and the Mastodon API handles their end.

Vice versa, NodeBB would use its own API to render a /world feed.

@deadsuperhero@social.wedistribute.org @evan@cosocial.ca

@julian @deadsuperhero @evan

Can't help but wonder about terminology use and abstractions they indicate. Nowhere in the specs is there mention of 'timeline' and neither of 'feed' (except as example use in AS).

I feel we started with powerful specs to be able to model *any* social networking use case. But where the specs had blanks gradually the impls filled these in with leaky abstractions such that fedi is now hammered into a very narrow social media microblogging domain.

If an app needs "Timeline" and "Feed" concepts, then it should model them. Given the actor-based nature of AP they might be actors, or whatever is best. These concept are about solution development, i.e. what is built on top of the protocol, and not indicative of core protocol capabilities.

There's so much confusion on "where does the protocol end vs. where does my app design start".

SDK's should offer "Addressable actors exchanging msgs with object payload", and hide all impl details for the solution developer.

@smallcircles @julian @deadsuperhero we call them collections.

https://www.w3.org/TR/activitypub/#collections

@smallcircles @julian @deadsuperhero we call them collections.

https://www.w3.org/TR/activitypub/#collections

@evan@cosocial.ca gosh I can't imagine assigning Add and Remove activities for a "popular" collection. It changes so often that it seems a waste of resources to try to track it.

Dynamic Collection?

Or as @smallcircles@social.coop said, even just light algorithmic ordering in a timeline makes stuffing it into a collection unwieldy.

@julian

I might not understand what we're talking about.

@smallcircles said that AP doesn't mention "timelines" or "feeds". We use a different term, collections. They are ordered in reverse chronological order, like what most people expect a "feed" to look like.

@julian

I haven't seen anyone use Add and Remove activities to notify updates to the `outbox`. I don't think it would work; it's too recursive.

I've done it for other feeds, like `replies` or `followers`, and it works pretty well.

@smallcircles

@evan @julian@activitypub.space @smallcircles Mind if I butt in here with a question about management of the `replies` collection? I'm looking at this for the interaction controls FEP draft.

GoToSocial currently broadcasts an `Accept(Note)` to let followers know a reply has been accepted (see https://docs.gotosocial.org/en/latest/federation/interaction_controls/#broadcasting-accepts-for-the-benefit-of-third-servers). We'd want to add an inverse for revocation, which would be `Undo(Accept(Note))` imo.

I feel `Add` and `Remove` on the `replies` collection may be more idiomatic and, in a sense, easier. Opinions?

@evan @julian @deadsuperhero

Except when they are called other names instead

A timeline is a different thing than a collection imho. And an AS collection has some very particular functionality, which if I model a timeline in my app may not supported (e.g. reverse ordering).

Collection / 'timeline' is one of those words where sometimes they indicate an app domain, and sometimes a core protocol mechanism. Same is true with 'follow' which is sometimes a user action, sometimes indicates low-level publish/subscribe.

For core capabilities that must be part of the specs, in 'protocol space' it may be better to use terminology that is more common in messaging architectures and all the various architecture patterns that are involved. Perhaps idk we deal with a time-ordered event log or something like that.

@smallcircles @evan An AS2 Collection cannot be a timeline (in general). It’s not even ordered. An AS2 OrderedCollection (a subtype of Collection) might be ordered by time or not, so it’s also not a timeline (in general). When they are ordered by some time value (unspecified in AP) they are often called “streams” in the spec. The Mastodon content timelines are not the same as AP activity streams although a filtered AP stream can be transformed to a content timeline.

@steve I think
we need to emphasize that timelines can be built from regular collections, even unordered ones, by using some intermediate representations specific to the type of timeline that a client wants to render.

The fact that the specification does not directly support a mapping between a collection and a responsive timeline, *DOES NOT MEAN* one can't be built from it, only that it requires a little more effort on the client side.

My goto example is how rich mail clients allow responsive mailbox representations on top of a much less expressive collection method that IMAP provides compared to ActivityPub.

@smallcircles @evan

@mariusor @smallcircles @evan I’m not sure I completely follow. A timeline is ordered by time. I agree that an unordered collection could be sorted by time to create a timeline. The AP OrderedCollection “stream” is a kind of rigid presorting that anticipates what an AP client would want. However, I also agree that even those could be reordered (by time or otherwise) and/or filtered in the client to provide custom views of the activity stream.

@steve yes, that's how I meant it. A client fetches as much of the collection as it can, then applies whatever rules it wants to transform the result into a "timeline" when the user asks for it.

This however most likely requires local caching of the collection to have decent latency.

@smallcircles @evan

@mariusor @smallcircles @evan Yes, it can be done in the client or the server, or both. I’d like to see an interoperable way to define custom timelines (a kind of user-defined timeline algo) that the server maintains. A Mastodon account list timeline is a super simple version of it, but AP could provide something much more powerful (advanced filtering, merging, ranking, …). Ideally, these could be shared and customized further on the client side.

@steve frankly I disagree with this point. Servers should be simple. We need to move away from the paradigm of custom purpose ActivityPub servers that Mastodon pushed where the client and server are the same service.

Timelines should be orthogonal to the ActivityPub specification and, in my opinion, kept well away from it.

What's the benefit for my client application to know what your server's preferred timeline representation is?

Let's not go down the path where everything looks like a nail because we really like hammers.

@smallcircles @evan

@mariusor @smallcircles @evan I think you read something other than what I wrote. . I’m describing *user-defined* timelines where the heavy lifting is done in a server. That server would be (or could be) *general purpose* and not specific to an activity domain. I definitely wasn’t suggesting a monolithic, tightly-coupled client/server architecture. I want my timeline definitions to be portable and interoperable.

@steve apologies, I take "server" in the context of ActivityPub discussion to be an "ActivityPub server", not all the other web-servers involved in the process.

And when I say "client", I mean a "consumer of ActivityPub", which as you say, many times is also a web server.

@smallcircles @evan

@mariusor @steve @evan

> And when I say "client", I mean a "consumer of ActivityPub", which as you say, many times is also a web server.

Indeed. Another term that I see people use in different meaning, also when talking about C2S.

In one meaning the user device is referred to, that you might need to hole-punch with to have a full AP server, or which depends on a server relay.

And the other meaning as role. As in client/server roles, pure conceptual, and which might swap too.

@smallcircles @evan An AS2 Collection cannot be a timeline (in general). It’s not even ordered. An AS2 OrderedCollection (a subtype of Collection) might be ordered by time or not, so it’s also not a timeline (in general). When they are ordered by some time value (unspecified in AP) they are often called “streams” in the spec. The Mastodon content timelines are not the same as AP activity streams although a filtered AP stream can be transformed to a content timeline.