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

# Domains Overview

> Schema reference for Domains entities

Domains are the highest level of the OpenAlex topic hierarchy. There are only 4 domains, each containing multiple fields: Life Sciences, Social Sciences, Physical Sciences, and Health Sciences.

The topic hierarchy is: **Domain** → Field → Subfield → Topic

## Filter, sort, and group\_by fields

The API supports filtering, sorting, and grouping on domains fields. See [Filtering](/guides/filtering), [Sorting](/guides/sort), and [Grouping](/guides/grouping) for syntax.

Fields marked **(deprecated)** are `.search` filters — use the [`search` parameter](/guides/searching) instead.

| Field                                  | Sort | Group\_by | Filter |
| -------------------------------------- | :--: | :-------: | :----: |
| `cited_by_count`                       |   ✓  |     ✓     |    ✓   |
| `default.search` **(deprecated)**      |      |           |    ✓   |
| `display_name`                         |   ✓  |           |    ✓   |
| `display_name.search` **(deprecated)** |      |           |    ✓   |
| `fields.id`                            |   ✓  |     ✓     |    ✓   |
| `from_created_date`                    |   ✓  |           |    ✓   |
| `id`                                   |   ✓  |     ✓     |    ✓   |
| `works_count`                          |   ✓  |     ✓     |    ✓   |