abi
abi•2y ago

JSON Schema Core, $dynamicAnchor, and $vocabulary

Slightly off-topic, but I'm writing a Deno library. Anyone deeply knowledgeable on JSON Schema Core? I have this meta-schema, and I can't figure out how the heck it's supposed to work that "$ref": "meta/core" would refer to "https://json-schema.org/draft/2020-12/vocab/core" – any ideas? I feel like I'm missing something fundamental knowledge on the JSON Schema Core spec here... 
{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "$id": "https://json-schema.org/draft/2020-12/schema",
    "$vocabulary": {
        "https://json-schema.org/draft/2020-12/vocab/core": true,
        "https://json-schema.org/draft/2020-12/vocab/applicator": true,
        "https://json-schema.org/draft/2020-12/vocab/unevaluated": true,
        "https://json-schema.org/draft/2020-12/vocab/validation": true,
        "https://json-schema.org/draft/2020-12/vocab/meta-data": true,
        "https://json-schema.org/draft/2020-12/vocab/format-annotation": true,
        "https://json-schema.org/draft/2020-12/vocab/content": true
    },
    "$dynamicAnchor": "meta",
    "title": "Core and Validation specifications meta-schema",
    "allOf": [
        {"$ref": "meta/core"},
        {"$ref": "meta/applicator"},
        {"$ref": "meta/unevaluated"},
        {"$ref": "meta/validation"},
        {"$ref": "meta/meta-data"},
        {"$ref": "meta/format-annotation"},
        {"$ref": "meta/content"}
    ],
...
{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "$id": "https://json-schema.org/draft/2020-12/schema",
    "$vocabulary": {
        "https://json-schema.org/draft/2020-12/vocab/core": true,
        "https://json-schema.org/draft/2020-12/vocab/applicator": true,
        "https://json-schema.org/draft/2020-12/vocab/unevaluated": true,
        "https://json-schema.org/draft/2020-12/vocab/validation": true,
        "https://json-schema.org/draft/2020-12/vocab/meta-data": true,
        "https://json-schema.org/draft/2020-12/vocab/format-annotation": true,
        "https://json-schema.org/draft/2020-12/vocab/content": true
    },
    "$dynamicAnchor": "meta",
    "title": "Core and Validation specifications meta-schema",
    "allOf": [
        {"$ref": "meta/core"},
        {"$ref": "meta/applicator"},
        {"$ref": "meta/unevaluated"},
        {"$ref": "meta/validation"},
        {"$ref": "meta/meta-data"},
        {"$ref": "meta/format-annotation"},
        {"$ref": "meta/content"}
    ],
...
3 Replies
ioB
ioB•2y ago
Isn't the vocab and the allOf aligned one-to-one? JSON is ordered mostly by insertion time so it seems pretty easy to match the two up.
abi
abi•2y ago
>Isn't the vocab and the allOf aligned one-to-one? i mean... yes, but the syntax in each $ref seems completely arbitrary. the json schema core spec doesn't say anything about such a syntax that i'm aware. https://datatracker.ietf.org/doc/html/draft-bhutton-json-schema-00#appendix-D.2
IETF Datatracker
JSON Schema: A Media Type for Describing JSON Documents
JSON Schema defines the media type "application/schema+json", a JSON- based format for describing the structure of JSON data. JSON Schema asserts what a JSON document must look like, ways to extract information from it, and how to interact with it. The "application/ schema-instance+json" media type provides additional feature-rich integration wi...
abi
abi•2y ago
from the link: 
...
    "$dynamicAnchor": "meta",
    "$vocabulary": {
      "https://json-schema.org/draft/2020-12/vocab/core": true,
      "https://json-schema.org/draft/2020-12/vocab/applicator": true,
      "https://json-schema.org/draft/2020-12/vocab/validation": true,
      "https://example.com/vocab/example-vocab": true
    },
    "allOf": [
      {"$ref": "https://json-schema.org/draft/2020-12/meta/core"},
      {"$ref": "https://json-schema.org/draft/2020-12/meta/applicator"},
...
...
    "$dynamicAnchor": "meta",
    "$vocabulary": {
      "https://json-schema.org/draft/2020-12/vocab/core": true,
      "https://json-schema.org/draft/2020-12/vocab/applicator": true,
      "https://json-schema.org/draft/2020-12/vocab/validation": true,
      "https://example.com/vocab/example-vocab": true
    },
    "allOf": [
      {"$ref": "https://json-schema.org/draft/2020-12/meta/core"},
      {"$ref": "https://json-schema.org/draft/2020-12/meta/applicator"},
...
hm, i think i get it now. "$id": "https://json-schema.org/draft/2020-12/schema", this identifies the URI of the schema itself. so then the relative URI meta/core becomes: https://json-schema.org/draft/2020-12/meta/core which is what's actually being $ref'd here. the vocabulary URI's themselves aren't actually schemas, more like unique identifiers.