A database structure that ties together relationships between data much more thoroughly than a relational database (RDBMS). There are fewer restraints, and data elements can be linked in almost any manner. When using a relational or NoSQL database, this connectedness has to be programmed into the queries and applications in order to derive the same results.
Ranking 20 graph databases in March 2016, DB-Engines.com listed Neo4j, OrientDB, Titan, Virtuoso and ArangoDB as the top five. See relational database