Data Resource JSON schema definition for `schema` seems to contradict specification

Overview

Problem description

Caution: there’s a lot of different uses of “schema” coming, so bear with me…

In the JSON schema definition file for a resource, data-resource.json, the formal definition for a schema property of a Resource is:

"schema": {
  "propertyOrder": 40,
  "title": "Schema",
  "description": "A schema for this resource.",
  "type": "object"
},

This allows only JSON-objects as schema definitions, essentially JSON-Strings. It disallows URLs or file paths.

This seemingly contradicts the human-readable specification of a schema property:

The value for the schema property on a resource MUST be an object representing the schema OR a string that identifies the location of the schema.

(Emphasis mine).

Proposed fix

I believe the section should read:

"oneOf": [
    {
      "title": "Schema path",
      "description": "A fully qualified URL, or a POSIX file path..",
      "type": "string"
    },
    {
      "title": "Schema as JSON",
      "description": "A schema encoded as a JSON object",
      "type": "object"
    }
]

I am no specialist for JSON schema, but if I change it, the Java implementation works with schema properties that are URLs and file paths.

How to reproduce

Reproduce the buggy behavior

• Head to https://www.jsonschemavalidator.net/

• copy the JSON content from https://frictionlessdata.io/schemas/data-resource.json into the “Schema” field on the left

• Copy into “Input JSON” on the right the following JSON:

   {
    "name": "test",
    "schema": "https://raw.githubusercontent.com/frictionlessdata/datapackage-java/master/src/test/resources/fixtures/schema/population_schema.json",
    "path": "https://raw.githubusercontent.com/frictionlessdata/datapackage-java/master/src/test/resources/fixtures/data/cities.csv"
   }
  

Result: validation will fail with the following error:

Found 1 error(s) Message: Invalid type. Expected Object but got String. Schema path: #/properties/schema/type

Reproduce the proposed fix

• Insert the proposed fix into the schema JSON
• Run validation against the same JSON snippet

Result: no validation error will be shown.

Fix to YAML source

Created a pull request, please check and if working, merge

[lwinfree]

Thanks @iSnow! @rufuspollock + @pwalsh what do you think?

[krassowski]

Does the path need to be to a JSON file with schema, or schema in a yaml file is good too?