In order to achieve multi-model database functionality, Cosmos DB supports the ARS model. The ARS model provides a very low-level data format, which can be used by any other databases or programming languages.

Atoms consist of a set of primitive data types such as number, string, and Boolean. Records consist of structure (set of primitive data types) and sequences that are arrays that hold atoms and records.

The data stored in this way is then used by your top-level databases such as Document DB, MongoDB, and tables. So, in layman's terms, whatever data you create using any of the Cosmos DB APIs is first converted into an ARS model and then stored in various regions.

This standard means of data storage opens up many opportunities. First, you can migrate or change the data model on the fly. Second, you scale and distribute it anywhere in the supported regions because the data model is technically the same for each database.

If you want more in-depth information about ARS, then refer to this official technical documentation page https://azure.microsoft.com/en-in/blog/a-technical-overview-of-azure-cosmos-db/.

Let's go ahead and dive deeper into each database model. First, you will learn DocumentDB API.