Require exactly one type for all resources

[azaroth42]

#1131 suggests that all relationships that can ever have more than one value must always be an array.
This is possible in the JSON-LD context by using @container:@set. It will be possible for language tagged strings in languagemaps in JSON-LD 1.1.

The current definition of type (@type, rdf:type) is that all resources must have at least one type, not exactly one type. Thus, by #1131, it should always be an array.

However, as per #1106, it is not possible to re-define the behavior of @type, you can only add aliases to it, like type. Meaning that I believe it is invalid to assert @container:@set for @type... and we would be inconsistent. The definition of @type is in this section of JSON-LD: https://www.w3.org/TR/json-ld/#node-objects

Given that we have not come across any use cases for multiple types in 5 years, I propose that the solution is to require exactly one type for every resource.

[tomcrane]

👍

[azaroth42]

Urgh, just realised that the same applies to @context when used in inline resources.

If you have a Image service, with an extension, you would need:

"service": {
  "@context": ["http://example.org/extension/context.jsonld", 
    "http://iiif.io/api/image/3/context.json"],
  "id": "...",
  "height": 1000,
  "extension": "fish"
}

We can minimize this in JSON-LD 1.1 with the use of type and property specific contexts, but the above is still a problem.

[jpstroop]

Community Call on 7/5: Make the requirement to type-check the exception rather than the rule.

[azaroth42]

Reflected the issue to JSON-LD for W3C discussion: json-ld/json-ld.org#512

[azaroth42]

Discussion at Getty AV: 👍

[azaroth42]

Further discussion: Need to distinguish between URIs and Resources (e.g. profile URIs don't need types, but licenses do)
Web-Annotation / IIIF inconsistency that annotation bodies (for example) don't require types... but not a conflict, we would just be more restrictive.

[zimeon]

👍 agreed at Toronto WG meeting

[christopher-johnson]

How do you intend to handle structures like this with only one type?

"resource":{
        "@id": "http://example.org/iiif/book1/res/music.mp3",
        "@type": "dctypes:Sound",
        "format": "audio/mpeg"
      }

http://example.org/iiif/book1/res/music.mp3 has at least two types, an oa:hasBody and a dctypes:Sound. The class of an object property (as an instance of some class) is transitive to the object implicitly.

ref: #1280

[azaroth42]

Done: http://prezi3.iiif.io/api/presentation/3.0/#type

(Noting small typo, missing a space)

[azaroth42]

@christopher-johnson Indeed implicitly. One explicit type in the serialization.

[zimeon]

Agree done but I think we should fix typo before closing... PR #1294