Add qualifiedRelations

[nichtich]

There is a use case to express connections between entities with qualifiers, e.g.

• a person had membership in an organization at specific time
• a person married another person at a specific time at a specific location
• ...

This can be modeled similar to Wikibase data model in JSON:

{
  "qualifiedRelations": {
    "http://example.org/relations/membership": {
      "prefLabel": { "en": "member of", "de": "Mitgliedschaft" },
      "claims": [
        {
          "resource": { "uri": "http://example.org/org/party1" },
          "startDate": "2021-12-07"
          "endDate": "2021-12-07"
        },
        {
          "resource": { "uri": "http://example.org/org/party2" },
          "startDate": "2021-12-08",
          "rank": "preferred"
        }
      ]
    }
  }
}

A list of qualifiers (here startDate and endDate needs to be defined).

This could be extended to statement with object type other than resource (e.g. number of habitants, geographic coordinates...).

Documentation should explain differences to Wikibase data model as well:

• JSKOS optionally includes the name of the property (e.g. "member of"). Wikibase only stores the identfier.
• Wikibase allows arbitrary qualifiers. JSKOS has a fixed list of qualifiers.
• Wikibase has special encoding for "no value" and "some value"
• Wikibase further supports references of statements
• Wikibase JSON uses "claims" with different semantics, better use "values" or another name?

[StiftungAusNachlass]

I am happy to attach the first scribble (for documentation)

[nichtich]

DANTE fields to also cover (TODO: define/find property URIs for these):

• profession
• religion (of a person)
• member of a party / organization
• nationality, ethnic affiliation
• specific type of a place (e.g. fictional, street, church...)

[nichtich]

Better use name qualifiedRelation. TODO: JSON-LD context to map to RDF.