oneOf types and value enumerations

[timothee-haudebourg]

Introduces value enumerations, a new enumeration layout for oneOf types that defines a surjection from the layout domain to the type domain.

For instance:

type T = { "Foo" => Foo, "Bar" => Bar }

This TreeLDR model defines

• the type { Foo, Bar } containing the two instances Foo and Bar.
• the layout { "Foo", "Bar" } containing the two string values "Foo" and "Bar".

Wildcard item.

type T = { "Foo" => Foo, "Bar" => Bar, * : tldr:String => rdfs:Class }

This TreeLDR model defines

• the type rdfs:Class that includes the two members Foo and Bar.
• the layout tldr:String with two outstanding values "Foo" and "Bar".

Advantages for the LD context generation.

For now the expected value of "@type" terms and the name of type scoped contexts is ill defined. By default type scoped contexts are not generated. It is enabled by the "hacky" --rdf-type-to-layout-name that allow the context generator to use layout names as term for type scoped contexts, even though it is not specified in the model.

Using value enumerations we could generate type scoped contexts consistently with the model definiton. For intstance:

layout Foo for T {
  rdf:type as "@type": required multiple &rdfs:Class,
  ex:prop: xsd:integer
}

would not generate a type scoped context since the IRI of T is expected for as "@type". However:

layout Foo for T {
  rdf:type as "@type": required multiple { "TermForFoo" => T, * : tldr:String => rdfs:Class },
  ex:prop: xsd:integer
}

would generate a type scoped context under the "TermForFoo" term like so:

{
  "TermForFoo": {
    "@id": "https://example.com/T",
    "@context": {
      "prop": "https://example.com/prop"
    }
  }
}