Type Coercion / Node Conversion: @coerce keyword or similar

I have an idea for a future version of JSON-LD.

As a web developer, I would like to receive a JSON document from i.e. a simple API, add a @context to it, and perform JSON-LD operations. This light approach has been a big selling point to me for using JSON-LD.

A common response from such an API may include an "id" property as a number (as it is indexed in the source database as an integer), so after applying the @context the document may look like this:

{
  "@context": {
    "@base": "http://starwars.com/",
    "@vocab": "http://starwars.com/",
    "id": "@id",
    "type": "@type"
  },
  "id": 123,
  "type": "Human",
  "firstName": "Luke",
  "lastName": "Skywalker"
}

Currently, the expansion step will generate an error:

Invalid JSON-LD syntax; "@id" value must a string.

My intention in declaring the @base was to form the IRI "http://starwars.com/123". I don't think this kind of type coercion is currently possible with JSON-LD.

The alternative would be a blank node with a custom ID property, which is less useful in certain situations.

I propose a solution that coerces the XSD type, so that when flattened, it becomes:

[
  {
    "@id": "http://starwars.com/123",
    "@type": [
      "http://starwars.com/Human"
    ],
    "http://starwars.com/firstName": [
      {
        "@value": "Luke"
      }
    ],
    "http://starwars.com/lastName": [
      {
        "@value": "Skywalker"
      }
    ]
  }
]

As a starting point, I suggest adding a keyword called @coerce.

I originally opened this as an issue in Framing and got some helpful feedback from @gkellogg:

https://github.com/w3c/json-ld-framing/issues/98

This would probably be in compaction/expansion rather than framing. It is somewhat similar to the useNativeTypes option for fromRdf.

It’s a common idiom in JSON, so it’s worthy of future consideration.

Review the JSON-LD 1.1 syntax around expansion and compaction, then read the referenced json-ld-framing issue for prior feedback. The proposed @coerce behavior and its placement need agreement; done means the specification defines the behavior and includes corresponding tests.