semantic ambiguity between Relationship.object and Activity.object

[trwnh]

in commenting on #666 i realized we don't have an issue for this filed already. this is maybe a subset of #666

Summary

as:object is used ambiguously on both as:Activity and as:Relationship.

as:object is defined like so:

When used within an Activity, describes the direct object of the activity. For instance, in the activity "John added a movie to his wishlist", the object of the activity is the movie added.

When used within a Relationship describes the entity to which the subject is related.

Domain: Activity | Relationship
Range: Object | Link

these are two different senses of the plain English word, "object".

one sense is grammatical -- in subject-verb-object form, the object is the noun that the verb acts upon. this is the Activity.object

one sense is mathematical -- the object is the end of a relationship between two entities. this is the Relationship.object

Possible approaches

next version / needs fep

• use a different IRI for Relationship.object (similar to Split mediaType into two properties; one for Link, one for Object? (contentType?) #638)
• reconsider Relationship and either refine it, or deprecate it, or some secret third thing (discussed more in Disjointness of reified classes (as:Link, as:Relationship, rdf:Statement, as:Activity) could be refined/reconsidered #666)

[evanp]

I see a few cases where this could be a problem:

1. Legibility for examples. If I'm reading the AV spec, and I see a Relationship with an object property, and I'm used to Activity objects from other situations, I might mistakenly think that object in this situation is the same. That's definitely worth considering.
2. Ambiguity for interpretation of the property within a single object. If we have a multi-typed object, Follow and Relationship, it would be hard to decide what the object actually means. (I don't think that's a good representation, but this is for example.)
3. Ducktyping when type is not set. If I have a JSON-LD object with only one object property, what is its inferred type? It could be a Relationship or an Activity, and there's no way to know.

These seem pretty niche, but worth considering. I like the idea of including other properties for subject and object.

I think that Relationship is underused and there are some very interesting connections we could make between actors on the Fediverse using this type. I'd like to keep it for that use, but I don't know if tinkering with it for the next version is worth it without some concrete applications.

[github-actions]

This issue has been labelled as potentially needing a FEP, and contributors are welcome to submit a FEP on the topic.
Note that issues may be closed without the FEP being created; that does not mean that the FEP is no longer needed.

[trwnh]

One fix is to make this change in the JSON-LD context document in a way that is completely transparent for JSON consumers, using type-scoped contexts:

{
  "@context": {
    "as": "https://www.w3.org/ns/activitystreams#",
    "object": {
      "@id": "as:object",
      "@type": "@id"
    },
    "Relationship": {
      "@id": "as:Relationship",
      "@context": {
        "object": {
          "@id": "_:objectOfRelationship",
          "@type": "@id"
        }
      }
    },
  }
}

the above is saying basically that:

• "object" is the term defined by AS2-Vocab right now;
• "Relationship" is the term defined by AS2-Vocab right now;
  • "object" in the context of a "Relationship" is a different thing

another thing that could be done is to define 2 new properties which are subproperties of as:object as currently defined:

_:objectOfActivity
  rdfs:subClassOf as:object;
  rdfs:domain as:Activity.

_:objectOfRelationship
  rdfs:subClassOf as:object;
  rdfs:domain as:Relationship.