Is this valid in #ActivityPub / AS2 ?

Steve Bate

Is this valid in #ActivityPub / AS2 ?
{
"@context": "https://www.w3.org/ns/activitystreams",
...
"tag": [
{
"type": "Hashtag",
"name": "example",
"href": "https://example.com/tag/example"
}
}
Note that "Hashtag" is not a term in the normative AP/AS2 context. It seems to break linked data processing, but it also seems to pass the JSON-LD compaction requirements of AS2 (based on the JSON-LD Playground). If true, this means you can use extended types without extending the context. ‍️

marius

@steve "valid" as in it triggers no failure cases: probably. "valid" as in someone knows what to do with it: probably not.

I base this on section 5 of the activitystreams core spec: https://www.w3.org/TR/activitystreams-core/#extensibility

Julian Fietkau

@steve Hashtag is part of this Community Group Report: "ActivityPub Miscellaneous Terms" https://swicg.github.io/miscellany/ I think the implication is that this will be added to the spec when the working group is fully spun up again, but it also defines a JSON-LD context for itself that you can use today if you want to be both compatible with Mastodon and compliant with JSON-LD.

Emelia 👸🏻

@steve it is in the miscellaneous terms document.

Steve Bate

@thisismissem @julian I'm aware of the unofficial term, but that wasn't my point. That term is not included in the example document's JSON-LD context (normative or otherwise). It doesn't seem like a good practice although there's an example like this in the ActivityPub book. Mastodon uses Hashtag, but it includes the term in the extended JSON-LD context. It appears that one can include *any* undefined type (and other terms?) without them being in the context and it's technically allowed.

Steve Bate

@mariusor Mastodon knows what to do with it even without the Mastodon/AP extensions in the context (it doesn't require the extensions to be in the context). However, it would require some patching of the AP document (or injection of additional context) prior to JSON-LD processing to be used by a linked data consumer.

naturzukunft

@steve i think you're not talking about tags, but about the example of using a type. but still, i have to mention that i would be very happy for us to talk about #skos before we describe advanced hashtags. You hit my hashtag nerve with your choice of example

infinite love ⴳ

@steve @thisismissem @julian this is due to

"@\vocab": "_:"

in the context document. it's a pre-JSON-LD 1.0 feature that got obsoleted by JSON-LD 1.0 and i think deprecated in JSON-LD 1.1?

https://www.w3.org/TR/json-ld11/#changes-from-cg and #h-note-0 and #h-note-41 say:

> The use of blank node identifiers to label properties is obsolete, and may be removed in a future version of JSON-LD, as is the support for generalized RDF Datasets.

https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node-identifier

> Blank node identifiers begin with _: