# What is Unity Catalog in Databricks?

Databricks' governance layer: one place that names every table, file volume, model and function as catalog.schema.object, decides who may use each, and records lineage and access.

- Page: https://tecyfy.com/concepts/unity-catalog
- Subject: Data engineering in the AI era (https://tecyfy.com/concepts)
- Level: beginner
- Also called: Databricks Unity Catalog, UC

A company's data platform holds thousands of tables, files and models, used by hundreds of people and, now, by AI agents. Without one place that knows what exists and who may touch it, every team keeps its own permissions and nobody can answer "who read the salary table last week?". Unity Catalog is that place on Databricks.

## A name for everything

Every asset gets a 3-part name: `catalog.schema.object`.

```sql
SELECT * FROM finance.payroll.salaries;
```

- A **catalog** is the top level, often one per business unit or environment (`finance`, `dev`, `prod`).
- A **schema** groups related objects inside it (`payroll`).
- An **object** is a table, a view, a volume of files, a function, a machine learning model or a served model.

The same names work from SQL, Python, notebooks, jobs and dashboards, in every workspace attached to the catalog.

## Who may use what

Permissions are granted on those objects:

```sql
GRANT SELECT ON TABLE finance.payroll.salaries TO `hr-analysts`;
```

Beyond plain grants, row filters and column masks hide rows or values from some users, and attribute-based policies apply a rule to every object with a tag, such as "mask anything tagged `pii`". Because the rule sits in the catalog, not in each tool, an analyst, a notebook and an AI agent asking the same question get the same answer with the same data hidden. For an agent, that makes the catalog a [Guardrail](https://tecyfy.com/concepts/guardrail) outside the model.

## Managed and external

A **managed** table's files live where Unity Catalog chooses, and it handles their whole life, including deleting them with the table. An **external** table points at files you manage; the catalog governs access but does not own the files. Newer features need managed tables: Databricks' multi-table transactions, for example, only write to managed [Delta](https://tecyfy.com/concepts/delta-lake) or Iceberg tables with catalog commits.

## Lineage and audit

Unity Catalog records [lineage](https://tecyfy.com/concepts/data-lineage) by itself: which tables fed which, down to the column, through to models and dashboards. When a source column changes, you can see every report and model downstream. An audit log, readable as a system table, records who accessed what.

## Open source too

Databricks also publishes Unity Catalog as an open source project, so other engines can use the same catalog interface. Workspaces created since November 2023 have it turned on by default, and most new Databricks features assume it.

## Related

- [Lakehouse](https://tecyfy.com/concepts/lakehouse): One store for all of an organisation's data: cheap files in cloud storage, as in a data lake, with the tables, transactions and fast queries of a data warehouse on top.
- [Data Lineage](https://tecyfy.com/concepts/data-lineage): The record of where a piece of data came from and everything it passed through, from source tables to the dashboards, models and AI answers built on it.
- [Delta Lake](https://tecyfy.com/concepts/delta-lake): An open table format that turns Parquet files in cloud storage into a table with transactions, a version history, schema checks, and updates and deletes, so a data lake behaves like a database.
- [Data Quality](https://tecyfy.com/concepts/data-quality): How far data can be trusted: complete, correct, on time and in the expected shape. Pipelines check it with rules and stop or flag rows that fail.
- [Guardrail](https://tecyfy.com/concepts/guardrail): Checks placed around a model that stop or change what goes in and what comes out, such as a filter on user messages or an approval step before an agent acts.

## Sources

- [What is Unity Catalog?](https://docs.databricks.com/aws/en/data-governance/unity-catalog/)
- [Transactions](https://docs.databricks.com/aws/en/transactions/)