Graph and ledger databases

For the final section of this chapter, we are going to study two more database types, one NoSQL and one a special type of database that can be made both with a SQL and NoSQL database, as we will see:

• Graph databases are used when you want to show the connections between items in your database. For example, consider Facebook and how they use friends of friends to help identify people you are likely to know and might want to connect with. This would be a good example of when a graph database could be a good option.
• Ledger databases are databases that keep track of every change that has ever been made. The database will never change any existing data but will add a new version next to the original. This can be very useful for systems such as bank transactions, where it is critical to have exceptional auditing controls.

Let's start by looking at graph databases.

Graph databases

Graph databases specialize in storing data in a manner...