Define "group"

[trwnh]

At present, there is no real difference between a Person / Group / Organization / etc within ActivityPub. All actors are defined loosely in terms of having an inbox and an outbox, plus some other recommended or optional properties like followers and so on. How an actor behaves is out-of-scope of AP itself, so an actor may send or receive Activities of any arbitrary shape, and these Activities have arbitrary side effects and behavioral expectations or assumptions.

In prior art, there is FOAF and vCard. A foaf:Group uses foaf:member to directly refer to agents considered to be part of the group. Similarly, a vcard:Group uses vcard:hasMember to directly refer to individuals considered to be part of the group. Loosely, the concept of a FOAF "agent" and a vCard "individual" are used roughly equivalently with each other, but not equivalently to the concept of an ActivityPub "actor".

From a data modeling perspective, we might define a members collection (see #6 for more) which is the AS2 way of indirectly referring to objects of a certain consideration. At a surface level, we can say that the members collection operates indirectly along the same general relationship as foaf:member and vcard:hasMember operate directly, and we might say that a "group" is "something that has members", perhaps with further qualifications such as those members generally being actors?

Also, the definition of a "group" needs to be distinct from the definition of an "organization" which might have members or might instead have sub-units. We probably need to decide whether work on "organizations" is in-scope or out-of-scope for this task force. At least within prior art from https://www.w3.org/TR/vocab-org/ we see that it is possible to reuse the concept of "member" for both groups and organizations.