JSON LD serialization from schema.org

Question

The following example is given on the json-ld playground.

Person example(expanded):

json-ld:

{
  "@context": "http://schema.org/",
  "@type": "Person",
  "name": "Jane Doe",
  "jobTitle": "Professor",
  "telephone": "(425) 123-4567",
  "url": "http://www.janedoe.com"
}

after serializtion to expanded:

[
  {
    "@type": [
      "http://schema.org/Person"
    ],
    "http://schema.org/jobTitle": [
      {
        "@value": "Professor"
      }
    ],
    "http://schema.org/name": [
      {
        "@value": "Jane Doe"
      }
    ],
    "http://schema.org/telephone": [
      {
        "@value": "(425) 123-4567"
      }
    ],
    "http://schema.org/url": [
      {
        "@id": "http://www.janedoe.com"
      }
    ]
  }
]

I ask myself where does the serializer gets the information to map the properties to the right subsequent schema (name). To achieve that, it must be able to get hold on to the person json ld schema. But if I go to https://schema.org/Person I get an HTML back and not a JSON-LD file.

So where does the serialization knowledge come from?

from @context

Jay Gray
– Jay Gray

2021-02-17 23:27:08 +00:00
Commented Feb 17, 2021 at 23:27 — Jay Gray
– Jay Gray, Commented Feb 17, 2021 at 23:27
But if i open schema.org i dont get a json file back

simibac
– simibac

2021-02-17 23:39:34 +00:00
Commented Feb 17, 2021 at 23:39 — simibac
– simibac, Commented Feb 17, 2021 at 23:39

Gregg Kellogg · Accepted Answer · 2021-02-18 00:17:09Z

3

Jay is correct that the knowledge comes from the @context. This can be specified in a couple of ways:

Inline, using an object value for @context (or an array, which includes an object),
By directly retrieving a context from the URL specified (e.g., https://json-ld.org/contexts/person.jsonld),
By having the server do context-negotiation on the request, as an HTTP request includes an Accept header preferring JSON-LD (see Interpreting JSON as JSON-LD) such as the following:
```
GET /ordinary-json-document.json HTTP/1.1
Host: example.com
Accept: application/ld+json,application/json,*/*;q=0.1
```
Or, as is presently deployed by schema.org, by returning a Link header along with a GET or HEAD request identifying the location of the actual context to load (See Alternate Document Location):
```
HTTP/1.1 200 OK
...
Content-Type: text/html
Link: <alternate.jsonld>; rel="alternate"; type="application/ld+json"
```
This last case is used by schema.org because of the challenges of making HTTP Content-Negotiation work properly on certain static site generators. If you to a HEAD request at https://schema.org, you'll get back headers including the following:

HTTP/2 200 
link: </docs/jsonldcontext.jsonld>; rel="alternate"; type="application/ld+json"

A conforming JSON-LD processor (such as on the json-ld.org playground) knows to follow this link to find the actual context.

In the case of the Person example, "Person" and the other keys are turned into IRIs based on instructions in that context file such as the following:

{
  "@context": {
    ...
    "schema": "http://schema.org/",
    "Person": {"@id": "schema:Person"},
    "name": { "@id": "schema:name"},
    "jobTitle": { "@id": "schema:jobTitle"},
    "telephone": { "@id": "schema:telephone"},
    "url": { "@id": "schema:url", "@type": "@id"},
    ...
  }
}

Note that in the case of "url", it also knows that the value of that property should be treated as an IRI, rather than a text string.

answered Feb 18, 2021 at 0:17

Gregg Kellogg

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2 Comments

simibac Over a year ago

Ok thank you, this clarifies a lot. Is my assumption correct, that the processor must maintain a list of different urls that must be resolved in different ways. If this assumption is true, why is this not standardised?

Gregg Kellogg Over a year ago

The JSON-LD spec describes all these processes. Content-Negotiation has a long history in RDF circles and is based on IETF standards. The link relation is new, but also comes from other specifications. URL resolution is only done for context retrieval.

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