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Self-describing JSON Schemas

This page is adapted from the Snowplow Analytics blog post, Introducing self-describing JSONs.

With the explosion of possible event types due to Snowplow going from a web analytics to a general event analytics platform, it became necessary to give some coherence to the events sent in to Snowplow. Snowplow dealing only with JSON, we chose to rely on JSON Schemas.

In addition to the usual JSON Schema we decided to make it self-describing by adding information we already knew about the schema such as:

  • vendor which tells us who created this JSON Schema
  • name which is the JSON Schema’s name
  • format in our case this will be a JSON Schema
  • version which is the JSON Schema’s version (using SchemaVer)

We encapsulated all this information in a self property.

As an example, we would go from this JSON Schema:

{
    "$schema": "http://json-schema.org/schema#",
    "type": "object",
    "properties": {
        "bannerId": {
            "type": "string"
        }
    },
    "required": ["bannerId"],
    "additionalProperties": false
}

to this one:

{
    "$schema": "http://iglucentral.com/schemas/com.snowplowanalytics.self-desc/schema/jsonschema/1-0-0#",
    "self": {
        "vendor": "com.snowplowanalytics",
        "name": "ad_click",
        "format": "jsonschema",
        "version": "1-0-0"
    },
    "type": "object",
    "properties": {
        "bannerId": {
            "type": "string"
        }
    },
    "required": ["bannerId"],
    "additionalProperties": false
}

incorporating the aforementioned self property.

Notice that we also changed the $schema property to our own JSON Schema which enforces the self property.

To make our JSONs self-describing we still have to reference this JSON Schema in our JSONs. This process is described in Self-describing JSONs.