json_schema: {
      "additionalProperties": false,
      "description": "common json schema for transaction volumes tagged by user channel and channel type (see DbD)",
      "properties": {
          "_id": {
              "description": "unique url-friendly base64 encoded, utf8 endoded concatenation identifier",
              "type": "string"
          },
          "_timestamp": {
              "_format": "date-time",
              "description": "ISO8601 combined date and time in UTC e.g. '2014-12-01T00:00:00+00:00'",
              "type": "string"
          },
          "channel": {
              "description": "user contact channel",
              "type": "string"
          },
          "channel_type": {
              "description": "class of channel for Dbd categrisation",
              "enum": [
                  "digital",
                  "non-digital",
                  "assisted-digital"
              ]
          },
          "count": {
              "description": "the number of completed transactions over the specific channel",
              "minimum": 0,
              "type": "integer"
          },
          "period": {
              "description": "The period covered by each data point from the _timestamp",
              "enum": [
                  "hour",
                  "day",
                  "week",
                  "month",
                  "quarter"
              ]
          }
      },
      "required": [
          "_id",
          "_timestamp",
          "period",
          "channel",
          "channel_type",
          "count"
      ],
      "title": "transactions-by-channel-type",
      "type": "object"
  }