A Cosmos DB data model is based on an Atom record sequence (ARS) data model. ARS is built to support multiple data models, such as column-based, key value, graph-based, and document-based. You will learn more about ARS in the next section.

At the time of writing this book, Cosmos DB supports the following data models:

• DocumentDB
• MongoDB
• Tables
• Graph
• Cassandra

The Microsoft Azure team is working on other data models too such as column based; they will release them soon!

DocumentDB is Microsoft's own document-based database also known as the NoSQL database. DocumentDB provides SQL query capabilities over schema-less document-based records. Cosmos DB provides an API and SDKs in various languages to integrate DocumentDB with your app! You will learn about it in the coming sections.

MongoDB is a very popular document store that has both an open source and enterprise version. MongoDB provides all complex operations such as aggregation, filter, and map-reduce over document store data. This is one of my favorite databases to start and ship any product faster. You will learn more about MongoDB in the coming sections.

Tables or table storage is Microsoft's version of Redis, a NoSQL-based key value store deployed as a service to hold petabytes of data and scale on the fly! You will learn more about it in the coming sections.

The graph is a database that consists of vertices and edges rather than key and value or column and rows. Graph databases are mainly used as a recommendation or suggestion feature. I am sure that you have used the People you may know feature of Facebook, that's graph! You will learn more about in the coming sections.

Cassandra is an open source, Apache licensed, distributed NoSQL database to mission-critical data with amazing durability and availability. Cassandra is proven and been used in some of the popular sites on the internet such as GitHub, Instagram, Reddit, eBay and CERN (not an internet site though). We will learn more about it in the coming section.

We will go deeper into each data model, but let's first look at what ARS is all about!