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

# About the Kelmarsh example

> Learn about the Kelmarsh wind farm sample data and how the Cognite Data Fusion (CDF) migration plugin guides use it.

<Warning>
  The migration plugin is an experimental feature. Updates to the Cognite Toolkit are likely to introduce changes to the described commands and processes.
</Warning>

The migration plugin guides use the **Kelmarsh** example throughout. Kelmarsh is a sample data set for a UK-based wind farm. The source data is available from [Zenodo](https://zenodo.org/records/5841834#.YgpBQ_so-V7).

## Why this example

Reusing the same assets, time series, and events in every procedure makes it easier to follow CSV mappings, lineage screenshots, and command output. When you see `source_data`, `zenodo`, or a wind turbine external ID in a later guide, it refers to this data set.

## What's in the data set

The data set has a root asset for the wind farm and six wind turbine assets of the same type. Each wind turbine has 298 time series and about 3,000–6,000 events.

The time series contain measurements such as wind speed, power output, and temperature. The events contain alarms and changes in operations, such as wind below minimum operating speed.

## How the guides use this example

This asset definition for one of the wind turbines shows the `source` and `dataSetExternalId` values the plugin maps during migration:

```yaml title="Kelmarsh1.Asset.yaml" theme={"languages":{"custom":["/_languages/kuiper.json","../_languages/kuiper.json"]}}
externalId: SEN 93420
name: Kelmarsh 1
parentExternalId: Kelmarsh
metadata:
  Alternative Title: KWF1
  Manufacturer: Senvion
  Model: MM92
  Rated power (kW): '2050'
  Hub Height (m): '78.5'
  Rotor Diameter (m): '92'
  Latitude: '52.400604'
  Longitude: '-0.947133'
  Elevation (m): '145.598'
  Country: UK
  Commercial Operations Date: 15/04/2016
source: zenodo
dataSetExternalId: source_data
```

The `source` value `zenodo` is what the migration plugin uses when it creates a `CogniteSourceSystem` node. The `dataSetExternalId` `source_data` is what it uses when it creates an instance space.

In Cognite Data Fusion (CDF), the asset hierarchy is a root **Kelmarsh** asset with six child wind turbines:

<Frame>
  <img class="illustration" src="https://apps-cdn.cogniteapp.com/@cognite/docs-portal-images/1.0.0/images/cdf/cdf_deploy/cdf_toolkit/migration-plugin/migration_classic_kelmash.png" alt="Kelmarsh wind farm asset hierarchy in CDF, with a root asset and six wind turbines" width="100%" />
</Frame>

[Migrating assets](/cdf/deploy/cdf_toolkit/guides/plugins/migration_plugin/assets) maps the root asset to a `KelmarshAsset` view and the turbines to a `WindTurbine` view. That split is why several procedures use a CSV file instead of migrating an entire data set to a single view.

## Further reading

* [Migration overview](/cdf/deploy/cdf_toolkit/guides/plugins/migration_plugin/steps)
* [Creating a data model and mappings](/cdf/deploy/cdf_toolkit/guides/plugins/migration_plugin/data_model_migration)
* [Known limitations](/cdf/deploy/cdf_toolkit/guides/plugins/migration_plugin/known_limitations)