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    content: Diplodoc Platform v5.52.0
alternate:
  - https://ydb.tech/docs/en/concepts/datamodel/cluster-namespace.md?version=v26.1
  - https://ydb.tech/docs/ru/concepts/datamodel/cluster-namespace.md?version=v26.1
  - href: en/concepts/datamodel/cluster-namespace.md
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    title: Markdown version
  - href: ../../llms.txt
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    title: llms.txt
sourcePath: en/core/concepts/datamodel/cluster-namespace.md
---
> **Documentation Index:** Fetch the complete configuration index at https://ydb.tech/docs/en/llms.txt

# Cluster Namespace and Object Naming

In YDB, all schema objects are organized into a hierarchical namespace called the **cluster schema**. This structure determines how databases, directories, and other objects are arranged and named, providing a clear and scalable way to manage data.

## Cluster Schema

The cluster schema forms a tree-like hierarchy where:

- The **root** represents the top level of the namespace.
- At the first level are [databases](https://ydb.tech/docs/en/concepts/glossary.md?version=v26.1#database).
- Inside each database, you can create nested [directories](https://ydb.tech/docs/en/concepts/datamodel/dir.md?version=v26.1) to build a custom hierarchy.
- [Schema objects](https://ydb.tech/docs/en/concepts/glossary.md?version=v26.1#scheme-object)—such as tables, views, and indexes—can reside either at the database root or within any directory.

![cluster schema diagram](_assets/cluster-scheme.png =500x)

## Naming Rules for Schema Objects {#object-naming-rules}

Every [schema object](https://ydb.tech/docs/en/concepts/glossary.md?version=v26.1#scheme-object) in YDB has a name. In YQL expressions, object names are used as identifiers, which can be unquoted or enclosed in backticks (`` ` ``). For details on identifier syntax, see [Keywords and identifiers](https://ydb.tech/docs/en/yql/reference/syntax/lexer.md?version=v26.1#keywords-and-ids).

Valid names for schema objects must meet the following criteria:

- **Allowed characters**:
  - Latin letters (`A–Z`, `a–z`)
  - Digits (`0–9`)
  - Special characters: `.`, `-`, and `_`
- **Maximum length**: 255 characters
- **Placement restrictions**: Objects cannot be created in directories with names that start with a dot (for example, `.sys`, `.metadata`, `.sys_health`)