Comparison of Relational Databases and Graph Databases
Can someone explain to me the advantages and disadvantages for a relation database such as MySQL compared to a graph database such as Neo4j?
In SQL you have multiple tables with various ids linking them. Then you have to join to connect the tables. From the perspective of a newbie why would you design the database to require a join rather than having the connections explicit as edges from the start as with a graph database. Conceptually it would make no sense to a newbie. Presumably there is a very technical but non-conceptual reason for this?
Answer
There actually is conceptual reasoning behind both styles. Wikipedia on the relational model and graph databases gives good overviews of this.
The primary difference is that in a graph database, the relationships are stored at the individual record level, while in a relational database, the structure is defined at a higher level (the table definitions).
This has important ramifications:
- A relational database is much faster when operating on huge numbers of records. In a graph database, each record has to be examined individually during a query in order to determine the structure of the data, while this is known ahead of time in a relational database.
- Relational databases use less storage space, because they don't have to store all of those relationships.
Storing all of the relationships at the individual-record level only makes sense if there is going to be a lot of variation in the relationships; otherwise you are just duplicating the same things over and over. This means that graph databases are well-suited to irregular, complex structures. But in the real world, most databases require regular, relatively simple structures. This is why relational databases predominate.