# Custom Datasets
You can implement the `Dataset` trait for any type to integrate custom data sources into your pipeline.
## The `Dataset` trait
```rust,ignore
pub trait Dataset: serde::Serialize {
type LoadItem;
type SaveItem;
type Error;
fn load(&self) -> Result<Self::LoadItem, Self::Error>;
fn save(&self, output: Self::SaveItem) -> Result<(), Self::Error>;
fn is_param(&self) -> bool { false }
#[cfg(feature = "std")]
fn html(&self) -> Option<String> { None }
}
```
## Example: a plain text dataset
```rust,ignore
#[derive(Serialize, Deserialize, Clone)]
pub struct TextDataset {
path: String,
}
impl Dataset for TextDataset {
type LoadItem = String;
type SaveItem = String;
type Error = PondError;
fn load(&self) -> Result<String, PondError> {
Ok(std::fs::read_to_string(&self.path)?)
}
fn save(&self, text: String) -> Result<(), PondError> {
std::fs::write(&self.path, text)?;
Ok(())
}
}
```
## Checklist
1. **Derive `Serialize`** (required by the supertrait) — and usually `Deserialize` too, so the catalog can be loaded from YAML.
2. **Name the type with a `Dataset` suffix** — the catalog indexer uses serde struct names ending in `"Dataset"` to identify leaf datasets. Without this suffix, nested struct fields may not be discovered correctly.
3. **Choose your error type** — use `PondError` for simplicity, or a custom error type if you want to preserve error detail (see [Dataset Errors](../error_handling/datasets.md)).
4. **Implement `html()`** (optional, `std` only) — return an HTML snippet for the viz dashboard. This is shown in the dataset detail panel.
## The `FileDataset` trait
If your dataset is backed by a file, implement `FileDataset` to enable use with `PartitionedDataset`:
```rust,ignore
pub trait FileDataset: Dataset + Clone {
fn path(&self) -> &str;
fn set_path(&mut self, path: &str);
}
```
This lets `PartitionedDataset` clone your dataset template and point each partition at a different file.