{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "title": "JSON Schema for IBM AI4Code GraphJSON Format",
  "description": "Prepared by Geert Janssen <geert@us.ibm.com>\nCopyright IBM Corporation 2020.",

  "type": "object",
  "properties": {
    "graph": { "$ref": "#/definitions/graph" }
  },
  "required": [ "graph" ],
  "additionalProperties": true,

  "definitions": {
    "graph": {
      "type": "object",
      "properties": {
        "version" : { "enum": [ "1.0" ] },
        "type":     {
          "description": "Indication of type, e.g. tree or dag.",
          "type": "string"
        },
        "directed": { "type": "boolean" },
        "label":    { "type": "string" },
        "root":  {
          "description": "Indication of the root node for a tree.",
          "$ref": "#/definitions/unsigned_or_string"
        },
        "order": { "enum": [ "none", "topological", "reverse-topological",
                             "dfs", "bfs" ] },
        "metadata": { "type": "object" },

        "nodes": {
          "description": "Mandatory node list.",
          "type": "array",
          "items": { "$ref": "#/definitions/node" }
        },
        "edges": {
          "description": "Mandatory edge list.",
          "type": "array",
          "items": { "$ref": "#/definitions/edge" }
        }
      },
      "required": [ "version", "directed", "nodes", "edges" ],
      "additionalProperties": true
    },

    "node": {
      "type": "object",
      "properties": {
        "id":       { "$ref": "#/definitions/unsigned_or_string" },
        "label":    { "type": "string" },
        "metadata": { "type": "object" }
      },
      "required": [ "id" ],
      "additionalProperties": true
    },

    "edge": {
      "description": "Edge object in an edge list.",
      "type": "object",
      "properties": {
        "id":    { "$ref": "#/definitions/unsigned_or_string" },
        "label": { "type": "string" },
        "between": {
          "description": "An ordered pair of 2 nodes.",
          "type": "array",
          "items": { "$ref": "#/definitions/unsigned_or_string" },
          "minItems": 2,
          "maxItems": 2
        },
        "metadata": { "type": "object" }
      },
      "required": [ "between" ],
      "additionalProperties": true
    },

    "unsigned_or_string": {
      "description" : "A non-negative integer or a string.",
      "oneOf": [
        { "type": "integer", "minimum": 0 },
        { "type": "string" }
      ]
    }
  }
}