# YAML Format Reference

This page describes the YAML format used by `dbtoyaml` and `yamltodb`.

## Top-level structure

```yaml
schema <name>:
  owner: <username>
  description: <text>
  table <name>:
    ...
```

## Schema properties

| Property | Type | Description |
|----------|------|-------------|
| `owner` | string | Schema owner |
| `description` | string | Schema comment |

## Table properties

| Property | Type | Description |
|----------|------|-------------|
| `owner` | string | Table owner |
| `description` | string | Table comment |
| `columns` | list | Column definitions (list of single-key maps) |
| `primary_key` | map | Primary key constraint |
| `foreign_keys` | map | Foreign key constraints |
| `check_constraints` | map | Check constraints |
| `unique_constraints` | map | Unique constraints |

## Column properties

| Property | Type | Description |
|----------|------|-------------|
| `type` | string | PostgreSQL data type |
| `not_null` | boolean | NOT NULL constraint |
| `default` | string | Default value expression |
| `description` | string | Column comment |

## Example

```yaml
schema public:
  table film:
    owner: postgres
    columns:
      - id:
          type: integer
          not_null: true
      - title:
          type: character varying(32)
          not_null: true
      - release_year:
          type: integer
          not_null: true
      - length:
          type: smallint
      - rating:
          type: character(5)
    primary_key:
      film_pkey:
        columns:
          - id
    check_constraints:
      film_length_check:
        columns:
          - length
        expression: ((length > 0) AND (length < 10000))
      film_release_year_check:
        columns:
          - release_year
        expression: (release_year >= 1888)
  owner: pg_database_owner
  description: standard public schema
```

The `columns` value is a list of single-key maps (one entry per column),
which matches the format produced by Pyrseas and is accepted by both
`yamltodb` implementations. `yamltodb` also accepts the equivalent map
form (`columns: {id: {...}, ...}`) for backward compatibility.