Graph or relational databases

A question arises as to whether the Discovery Data Service should use relational, property graph, document, or key value based database management systems  in its main patient record data stores.

This article considers the differences between graph and relational from the perspective of the known information requirements of health query. It reaches a conclusion as a result.

The starting point is to examine a few key logical differences then move on to some technical differences. Following this they are compared and contrasted from the perspective of the type of queries needed, in order to conclude which one to go for.

Firstly, its worth noting that a pure Graph model is not included for consideration. There are known problems at scale with pure graphs. If one were to adopt Graph then a property graph is the most likely variant. A property graph has properties on the nodes, and in the case of NEO4J, also has properties on the edges (which are called relationships).

Taking some very simple entity relationships from a health record, the following illustrates the different logical approach.  Graph is on the left, relational is on the right.