Digree: A middleware for a graph databases polystore

In this paper we present Digree, an experimental middleware system that can execute graph pattern matching queries over databases hosting voluminous graph datasets. First, we formally present the employed data model and the processes of re-writing a query into an equivalent set of subqueries and subsequently combining the partial results into the final result set. Our framework guarantees the correctness and completeness of the produced answers. Then, we present a prototype implementation of Digree, which is agnostic to the underlying data processing engines used at the endpoints. As the experimental results show, in many cases Digree outperforms a single node graph database deployment in execution speed, up to 20 times depending on the query type.