Data Structure

How Data is Structured in ArangoDB

The hierarchy that data is organized in is documents (data records) in collections, and collections in databases.

Documents

ArangoDB lets you store documents as JSON objects.

{
  "name": "ArangoDB",
  "tags": ["graph", "database", "NoSQL"],
  "scalable": true,
  "company": {
    "name": "ArangoDB Inc.",
    "founded": 2015
  }
}

Each record that you store is a JSON object at the top-level, also referred to as a document. Each key-value pair is called an attribute, comprised of the attribute name and the attribute value. Attributes can also be called properties or fields.

You can freely model your data using the available data types. Each document is self-contained and can thus have a unique structure. You do not need to define a schema upfront. However, sets of documents typically have some common attributes. If you want to enforce a specific structure, then you can do so with a schema validation.

Documents are internally stored in a binary format called VelocyPack .

Collections

Documents are stored in collections, similar to how files are stored in folders. A collection can hold an arbitrary number of documents.

You can group related documents together using collections, such as by entity type. For example, you can store book documents in a books collections. All book records have some common attributes like a title, author, and publisher. You can later create indexes for some of the often-used attributes to speed up queries. This is done at the collection level.

Databases

Each collection is part of a database. Databases allow you to isolate sets of collections from one another, usually for multi-tenant applications, where each of your clients has their own database to work with. You cannot run queries across several databases.

Every server instance has a default database called _system. It is special because it cannot be removed and it holds a couple of system collections that are used internally by the server. Other than that, you may create your own collections in this database like in any other.