It is complicated but there are good reasons for it. The historical advantage relational databases have over graph databases is that the former forces a more r

It is complicated but there are good reasons for it. The historical advantage relational databases have over graph databases is that the former forces a more restrictive representational structure onto the data model, which doesn't sound like an advantage at first. Restricting the ways in which a data model can be organized and traversed makes it straightforward to implement highly effective performance optimizations inside the database engine. Optimization is a tradeoff, by making one type of operation on a data model faster you often make another type of operation slower -- there is no free lunch. A database where all possible relationships in the data must be optimized is a database where little optimization is possible. The restrictions tacitly placed on relational database representations allow SELECT operations to be heavily optimized in a way that isn't possible if you want graph-like data model traversals to be fast and efficient. From the perspective of database internals, relational databases are optimized around SELECT performance and graph databases are optimized around JOIN performance. The former is intrinsically much easier to optimize. It turns out that shoe-horning data models into a relational database almost always has qualitatively better performance than using a more flexible graph database, and performance traditionally matters a great deal in databases. At a technical level, scaling ad hoc join operations -- the core operation of a graph database -- is famously extremely difficult. Ironically, most graph databases use data structures and algorithms that are tacitly optimized for the assumptions of a relational database implementation, that aren't trying to be good at graph-like things. You generally don't see graph databases that were designed from first principles to be a graph database; their internals are typically that of a relational database that supports join recursion. We figured out very early on how to optimize the hell out of relational databases. To this day we have been unable to build graph databases that are similarly optimized, partly because the computer science is much more difficult.