Alignment with Linked Data Notifications #3
Description
This is pretty closely related to #2
I want to start this discussion, but I admit that I have very little understanding of Linked Data Notifications (LDN). I will write down here what I could infer.
LDN self-describes as:
Linked Data Notifications is a protocol that describes how servers (receivers) can have messages pushed to them by applications (senders), as well as how other applications (consumers) may retrieve those messages. Any resource can advertise a receiving endpoint (Inbox) for the messages. Messages are expressed in RDF, and can contain any data.
Which sounds pretty similar to RDF Messages.
While it is not required reading to understand this specification, it is worth noting that ActivityPub's targeting and delivery mechanism overlaps with the Linked Data Notifications specification, and the two specifications may interoperably combined. In particular, the inbox property is the same between ActivityPub and Linked Data Notifications, and the targeting and delivery systems described in this document are supported by Linked Data Notifications. In addition to JSON-LD compacted ActivityStreams documents, Linked Data Notifications also supports a number of RDF serializations which are not required for ActivityPub implementations. However, ActivityPub implementations which wish to be more broadly compatible with Linked Data Notifications implementations may wish to support other RDF representations.
Which again makes sense – although aside from this informal note, there is no defined relationship between ActivityPub and LDN. So, formally, ActivityPub is NOT based on LDN – unless I missed something.
Back to LDN – it defines a specific, HTTP-based mechanism for discovering inboxes, sending notifications, consuming them, etc., all based on the Linked Data Platform. It does not define an abstract model of streams, mostly focusing on the exchange protocol.
On the other hand, RDF Messages focuses on the abstract model of streams and does not define a specific exchange/transmission mechanism.
In summary, I propose we simply view LDN as an RDF Message Stream implementation.