> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mezmo.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Pipeline Event Data Model

> How events move through a Pipeline via the event envelope, including the message, metadata, and timestamp fields and how to reference them.

## Event Envelope

When data is moving from Sources through Processors to Destinations in a Pipeline, the key details of these events come through the `message` object.

While this may be all you need in your Pipeline, there is other data that may be available to you in what we refer to as the **event envelope**.

### Envelope Fields

| Field       | Purpose                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| ----------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `message`   | The main field that carries the important data elements of an event. This field will always be present.<br /><br />Depending on the source, this field could be a string or an object.<br /><br />**Metrics:** while there is no prescribed schema for log events, metrics have a [prescribed data model](/telemetry-pipelines/metric-data-within-the-pipeline) you must follow.                                                                                                                                                  |
| `metadata`  | This field contains properties that describe the message. In most cases this data is only accessible in a Pipeline, and is not passed to the Destination.<br /><br />You can move Items in this field  into `message`  with the [Map Fields Processor](/telemetry-pipelines/map-fields-processor).                                                                                                                                                                                                                                |
| `timestamp` | This field is a ISO8601/RFC3339 formatted timestamp. For most Sources, this will be the date and time the event was received into the Pipeline.<br /><br />When there is a standard data format (OTLP, Auto-parsed logs in known formats, etc), Mezmo will set this field to the timestamp it finds in the standard field.<br /><br />You can override this value with the [Set Timestamp Processor](/telemetry-pipelines/set-timestamp-processor) or the [Script Execution Processor](/telemetry-pipelines/js-script-processor). |

```json theme={null}
{
  "message":{
    "bytes": 22322,
    "datetime": "24/Jan/2023:18:54:09",
    "host": "127.219.215.140",
    "method": "DELETE",
    "protocol": "HTTP/1.1",
    "referer": "https://names.de/apps/deploy",
    "request": "/secret-info/open-sesame",
    "status": "300",
    "user-identifier": "meln1ks",
    "data": {
      "extra-data": "mydata"
    }
  }
  "metadata":{
    "headers":{}
    "query":{}
  }
  "timestamp":"2024-06-28T19:41:00.995+00:00"
}

```

```json theme={null}
{
  "bytes": 22322,
  "datetime": "24/Jan/2023:18:54:09",
  "host": "127.219.215.140",
  "method": "DELETE",
  "protocol": "HTTP/1.1",
  "referer": "https://names.de/apps/deploy",
  "request": "/secret-info/open-sesame",
  "status": "300",
  "user-identifier": "meln1ks",
  "data": {
  	"extra-data": "mydata"
  }
}

```

### View Envelope Fields

You can view the contents of the envelope with the [Pipeline Tap and Simulation features. ](/telemetry-pipelines/view-pipeline-data)If it isn't displayed, make sure **Show data envelope** is set to **ON**.

<Frame caption="Data envelope display control set to **On**">
  <img src="https://mintcdn.com/mezmo-9a59581a/_0qiUj6KnOAKkTwu/images/telemetry-pipelines/qhfvo6nfja6ibkhklcyawsfoi5uraz2g8wl2ipwv8ou669e0032fl86ko12dtpx3.png?fit=max&auto=format&n=_0qiUj6KnOAKkTwu&q=85&s=33aa46df22125c151ffd1f915cad0262" alt="Image" width="199" height="45" data-path="images/telemetry-pipelines/qhfvo6nfja6ibkhklcyawsfoi5uraz2g8wl2ipwv8ou669e0032fl86ko12dtpx3.png" />
</Frame>

Fields in `message`, `metadata` and `timestamp` can be referenced in most processors and destinations. The message field also has a shortcut syntax of `.`

For example, to access `host` from the example above, you could reference it as `message.host` or `.host`