This database model is the collection of documents that contain all the necessary data records. You can customize the information written in the documents, group them and create database hierarchy managing documents instead of tables.
Such DBs are quite flexible. It might be of use when you need simpler data organization. The main difference from the relational database is that the document-oriented database uses a key (data item id) and a value (data item description) to structurize data. Apart from this, you can store some info in one document, instead of dividing it into several tables. Later we'll describe when to use MongoDB instead of MySQL.