NoSQL Terms

1) Data storage

Let's look at this relationship

Database ⊃ Collection ⊃ Document ⊃ Field

This means:

• A Database has many Collections
• A Collection has many Documents
• A Document has many Fields. Sometimes a Document is also called an Object.

This picture below is the mapping between terms related to data in Relational Database and NoSQL Database

2) Document

Unlike Relational Database in which each record is a row in a table, NoSQL stores each record as a document in JSON type.

This picture below is an example of a document in NoSQL database, in comparison with a row in RDB.

A few important things that differentiate between RDS and and NoSQL:

1. In RDB, the data type of a column is predefined and fixed in advance. For example, "Age" column in the example above must be Integer type. However, the data of "Age" field in NoSQL can be any types, such as String, Integer, Float.
2. Documents do not need to store the same fields.
   • For example, the picture BELOW shows two documents about WeatherData in the same collection. The right document has two additional fields: "timestamp" and "atmosphericPressureChange".
3. Nested document: one document can contain many inner document (object)
   • For example: "wind" field is an object itself, and it contains "direction" object.