Align JSON-LD output with DCAT

[LariDG]

In response to issue: #172 and discussions with Alejandra.

The JSON endpoints previously declared DCAT terms in the @context inconsistently, every response was a flat dcat:Dataset regardless of whether it was a catalogue listing, a dataset, or a glossary entry. This PR reshapes the responses to be more inline with DCAT usage.

Example of new structure after snippet put into json-ld playground:

http://localhost:8081/json/shots :

{
  "@type": "http://www.w3.org/ns/dcat#Catalog",
  "http://www.w3.org/ns/dcat#dataset": [
    {
      "@type": "http://www.w3.org/ns/dcat#Dataset",
      "http://purl.org/dc/terms/date": "2004-12-13T11:54:00",
      "http://purl.org/dc/terms/identifier": "219e5d59-b9dc-584f-b83b-018c47e8739d",
      "http://www.w3.org/ns/dcat#distribution": {
        "@type": "http://www.w3.org/ns/dcat#Distribution",
        "http://www.w3.org/ns/dcat#accessURL": "https://s3.echo.stfc.ac.uk/mast/level1/shots/11695.zarr",
        "http://www.w3.org/ns/dcat#downloadURL": "s3://mast/level1/shots/11695.zarr",
        "http://www.w3.org/ns/dcat#mediaType": "application/zarr"
      }
    },
    {
      "@type": "http://www.w3.org/ns/dcat#Dataset",
      "http://purl.org/dc/terms/date": "2004-12-13T12:07:00",
      "http://purl.org/dc/terms/identifier": "9ba69c96-34ac-5cd4-a1b8-8e9d7a44f871",
      "http://www.w3.org/ns/dcat#distribution": {
        "@type": "http://www.w3.org/ns/dcat#Distribution",
        "http://www.w3.org/ns/dcat#accessURL": "https://s3.echo.stfc.ac.uk/mast/level1/shots/11696.zarr",
        "http://www.w3.org/ns/dcat#downloadURL": "s3://mast/level1/shots/11696.zarr",
        "http://www.w3.org/ns/dcat#mediaType": "application/zarr"
      }

Single shot endpoint (http://localhost:8081/json/shots/11695):

{
  "@type": "http://www.w3.org/ns/dcat#Dataset",
  "http://purl.org/dc/terms/date": "2004-12-13T11:54:00",
  "http://purl.org/dc/terms/identifier": "219e5d59-b9dc-584f-b83b-018c47e8739d",
  "http://www.w3.org/ns/dcat#distribution": {
    "@type": "http://www.w3.org/ns/dcat#Distribution",
    "http://www.w3.org/ns/dcat#accessURL": "https://s3.echo.stfc.ac.uk/mast/level1/shots/11695.zarr",
    "http://www.w3.org/ns/dcat#downloadURL": "s3://mast/level1/shots/11695.zarr",
    "http://www.w3.org/ns/dcat#mediaType": "application/zarr"
  }
}

Due to cpf summary not being a dataset, changed the context to more appropriate definition:

{
  "@context": {
    "dct": "http://purl.org/dc/terms/",
    "schema": "https://schema.org/",
    "type": "@type",
    "name": "schema:name",
    "description": "dct:description"
  },
  "type": "schema:DefinedTermSet",
  "schema:hasDefinedTerm": [
    {
      "type": "schema:DefinedTerm",
      "description": "CP3c Set Volts",
      "name": "mcs_cp3c_volt"
    },
    {
      "type": "schema:DefinedTerm",
      "description": "Additive Gas Plenum",
      "name": "mcs_additive_gas_pressure"
    },

[LariDG]

@agbeltran I have made a start here on what we discussed. Please let me know if this is what you had in mind and if there are any changes you would like.

[agbeltran]

@LariDG this is looking really good, thank you! I'm pushing a few changes for create.py using rdflib so that the JSON-LD generated follows the namespaces and can be validated easily

Similar changes can be implemented to main.py

[agbeltran]

A few comments on remaining points: i) dcat:servesDataset should point to a dataset, so adding the service endpoints might be ok if they return datasets, ii) for the service URI, we should consider where the service is deployed (I only left localhost), iii) I tested the output in the json-ld playground, but we should test further and make sure everything is correct. Thanks!