Relational Database system:

Dis (advantages)

Relational databases have been around since the 1970s and are to this day the mostly used database type available. Lots of mature commercial as well as open-source implementations exist. High quality tooling exists which enables optimization or monitoring. To put it straight, the relational database has withstood the test of time and is probably not going anywhere anytime soon.

Related to the fact that these databases have been around for so much time, the community has had plenty of time to familiarize itself with the subject. Most developers have at least a basic understanding of SQL and there is plenty of information to find on the subject online.

A disadvantage of the relational databases is the fact that the data is divided into several tables, which sometimes have to be joined together. This takes a lot of time if the data size grows larger. We would have to have a separate query for each user to check the other users it’s connected with. In a high-density network that may develop overtime, this will cost more and more performance.

Graph Database system:

Dis (advantages)
The huge advantage of graph databases over relational databases is the performance gain when querying relationships between nodes. Since this is the prime functionality for a system such as this it can be used to meet the high performance demands that the stakeholders require from it.

Contrary to the relational databases, the technology has not been around for quite as long. This results in the fact that the amounts of developers that have a basic understanding of the concept are quite a lot slimmer than with relational databases. However, there are some implementations with an active user community such as Neo4j.

Big companies such as Google, Facebook and LinkedIn also use graph databases for their social networking data storage. This is good news for the field’s further development as these companies have the funds to support new research.

A further disadvantage is the fact that data storage takes 1.5 to 2 times as much room on a hard disk than in a relational database. This is not too much of an issue, since hard disk is very cheap nowadays but it is something worth mentioning.