how to use our own JSONLD in a custom field?

[VladimirAlexiev]

@tmberthold @jkbquabeck @SebastianOpriel please help:

We (@IvanIvanovOntotext and @skarampatakis) are trying this approach as a workaround for #1077 when adding a data Asset:

• At top level, use the restricted DCAT profile supported by EDC
• Inside a custom field, put our richer metadata:
  (DCAT, with dcat:DatasetSeries, with relations dcat:inSeries and prov:wasDerivedFrom, with CSVW...)

  "un:originalMetadata": {
        "@id": "bcca61be-e82e-4da6-bfec-9716a56cef35",
        "@type": "dcat:Dataset",  <<<
       ...
   },
  "https://w3id.org/edc/v0.0.1/ns/privateProperties": {},
  "@context": [
    "https://w3id.org/dspace/2024/1/context.json",
    {
      "@base": "https://dataspace.underpinproject.eu/",
      "edc": "https://w3id.org/edc/v0.0.1/ns/"
    }
  ]

We get this error:

[
    {
        "message": "There is no type alias registered for @type = http://www.w3.org/ns/dcat#Dataset",
        "type": "InvalidRequest",
        "path": null,
        "invalidValue": null
    }
]

If we remove the marked line, the error doesn't appear. But we really need

We tried these, to no avail:

• aliasing "type": "@type"
• pushing the context with network link "https://w3id.org/dspace/2024/1/context.json" inside un:originalMetadata
• next we'll try pushing our field inside "https://w3id.org/edc/v0.0.1/ns/privateProperties"

Please answer:

• what is the "no type alias registered for @type" error?
• does it look for @type at any nesting level of the JSON?
• is there a way to make it leave the custom field alone?
• is our only resort to store a CLOB (big string) in un:originalMetadata, and add JSON serialization/deserialization steps?

[IvanIvanovOntotext]

Pushing our field inside "https://w3id.org/edc/v0.0.1/ns/privateProperties" does not fulfill our goal because it gets ingested but cannot be retrieved so we cannot do it this way.
@skarampatakis proposed the only workaround that worked namely nesting our field one level more inside e.g. "un:underpinProperties": {"un:originalMetadata": {...}}