Allow XML, JSON, and RDF Data Resource

[nichtich]

Data Resources should not be limited to tabular data but also allow arbitrary XML files, JSON files, and RDF files. This requires extension of fields:

• type with xml, json, and rdf in addition to table.
• format for instance with xml (XML), json, yaml, ndjson, jsonl, json5... (JSON), ttl, nt, xml... (RDF)
• schema to reference an XML Schema (for XML), JSON Schema (for JSON), SHACL schema (for RDF)

[peterdesmet]

Agree.

• type: is a string with an enum that requires extension with new values
• format: is a string, no enum. so this can already be populated with xml, etc.
• schema: this is likely more complex, as it is specifically designed to reference a table schema.

[nichtich]

schema: this is likely more complex, as it is specifically designed to reference a table schema.

If type is not table, the semantics of schema field is not defined and the field can already contain an URL-or-Path, so an extension should be backwards-compatible.