# Message payload format for the EMQX broker on AWS IoT SiteWise Edge
<a name="connect-broker-payload-format"></a>

For the IoT SiteWise publisher component to consume data from your external application and publish it to the AWS IoT SiteWise cloud, the payload sent to the broker must meet specific requirements.

Understanding the payload format is key to successful MQTT communication with AWS IoT SiteWise Edge. While the connection setup process is covered in later sections, we present the payload requirements first to help you plan your implementation.

## MQTT topic requirements
<a name="connect-broker-mqtt-requirements"></a>

There are no restrictions on MQTT topic structure, including the number of levels or characters used. However, we recommend that the topic matches the `propertyAlias` field in the payload.

**Example property alias**  
If the MQTT topic is `site1/line1/compressor1/temperature`, ensure the `propertyAlias` matches.  

```
{
  "assetId": "compressor_asset_01",
  "propertyAlias": "site1/line1/compressor1/temperature",
  "propertyId": "temperature_sensor_01",
  "propertyValues": [
    {
      "quality": "GOOD",
      "timestamp": {
        "offsetInNanos": 0,
        "timeInSeconds": 1683000000
      },
      "value": {
        "doubleValue": 23.5
      }
    }
  ]
}
```

## JSON payload structure
<a name="connect-broker-json-payload"></a>

The MQTT message payload are written in JSON and follow the `PutAssetPropertyValueEntry` message format defined in the [AWS IoT SiteWise API Reference](https://docs.aws.amazon.com/iot-sitewise/latest/APIReference/API_PutAssetPropertyValueEntry.html).

```
{
   "assetId": "string",
   "propertyAlias": "string",
   "propertyId": "string",
   "propertyValues": [
      {
         "quality": "string",
         "timestamp": {
            "offsetInNanos": number,
            "timeInSeconds": number
         },
         "value": {
            "booleanValue": boolean,
            "doubleValue": number,
            "integerValue": number,
            "stringValue": "string"
         }
      }
   ]
}
```

**Note**  
For a message to be considered valid, only one of the following conditions can be true:  
The `propertyAlias` is set, or
Both `assetId` and `propertyId` are set
The `PutAssetPropertyValueEntry` has an `entryId` field that is not required in this context.