# Dataset schema diff

When metadata is re-ingested for a dataset, the platform compares the new revision to the previous one and surfaces every change — added columns, removed columns, renamed columns, type changes — on the dataset's **Structure** page. Operators get a visual diff for every revision, and the platform raises a [Backwards-incompatible schema change](/features/active-platform-features/alerting.md#backwards-incompatible-schema-change-what-triggers-it) alert whenever a removal or type change breaks downstream consumers.

This page covers the user-facing diff surface. The underlying alert mechanism — what triggers it, how it lifecycles, the per-entity halt configuration — lives on the [Alerting](/features/active-platform-features/alerting.md) page.

## Where to find it

Open any dataset (`Table`, `File`, `View`, `Vector Store`, ...) and navigate to the **Structure** tab on the entity's detail page.

<figure><img src="/files/TQ7yJ3HBM1cKGXpSgS0o" alt=""><figcaption><p>Dataset structure in the ODD UI</p></figcaption></figure>

The Structure tab carries:

* **Fields** — every column the dataset exposes.
* **Data types** per field.
* **Statistics** per field (when ingested by an adapter that emits them — see [Test Results Import](/features/data-quality/test-results-import.md) for the per-adapter coverage).

## Revision history

Every re-ingest of a dataset that **changes the structure** creates a new **revision**. Adding a column, deleting a column, renaming a column, or changing a column's data type all bump the revision counter. Same-structure re-ingests do not create a new revision (the platform compares structure by `(field_oddrn, type)` to decide).

The revision history is browsable per dataset: pick any two revisions to see exactly what changed between them.

<figure><img src="/files/jerumYZg9ynGN0QgJfUZ" alt=""><figcaption><p>Dataset revisions in the ODD UI</p></figcaption></figure>

Two illustrative diffs the platform surfaces:

<figure><img src="/files/oYjeYJ5Pv06xfkF84WaH" alt=""><figcaption><p>Column was added</p></figcaption></figure>

<figure><img src="/files/IfAwQr2ZSDKmWpkDHnzz" alt=""><figcaption><p>Column was removed</p></figcaption></figure>

The diff also captures **data-type changes** and **column renames** (both are detected as a type change or an ODDRN change between revisions, respectively).

## Backwards-incompatible alerts

When the comparison surfaces a **removal** of a previously-present column, or a **type change** on an existing column, the platform additionally raises a [Backwards-incompatible schema change](/features/active-platform-features/alerting.md#backwards-incompatible-schema-change-what-triggers-it) alert against the dataset. The alert lands on the entity's Alerts tab and the platform-wide [Alerts](/features/active-platform-features/alerting.md) section, and is **not** auto-resolved — an operator must work it by hand.

<figure><img src="/files/EJKXqLhasjgS1j29Im1V" alt=""><figcaption><p>Schema-change alerts in the ODD UI</p></figcaption></figure>

This separation is intentional:

* **The diff** is a discovery surface — every operator looking at the dataset sees what changed across revisions.
* **The alert** is the action surface — the platform proactively flags the case where the change breaks a downstream consumer.

For the full alert rule (what counts as backwards-incompatible per entity class — Datasets, Transformers, Consumers — and the first-ingest-no-alert exception), see [Alerting → Backwards-incompatible schema change](/features/active-platform-features/alerting.md#backwards-incompatible-schema-change-what-triggers-it).

## Activity-feed surfacing

Schema changes also surface as events on the [Activity Feed](/features/active-platform-features/activity-feed.md) — an operator walking the feed sees every metadata change across the catalog including schema edits, alongside ownership / tag / term / status changes.

## Where to next

* [Alerting → Backwards-incompatible schema change](/features/active-platform-features/alerting.md#backwards-incompatible-schema-change-what-triggers-it) — the alert rule, lifecycle, and operator workflow.
* [Activity Feed](/features/active-platform-features/activity-feed.md) — the audit trail of every schema (and other metadata) change.
* [Test Results Import](/features/data-quality/test-results-import.md) — per-adapter coverage of field statistics surfaced on the Structure tab.
* [Data Discovery overview](/features/data-discovery.md) — the bucket landing this page sits under.


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