Neo4j is a graph database. It is an embedded, disk-based, fully transactional Java persistence engine that stores data structured in graphs rather than in tables. A graph (mathematical lingo for a network) is a flexible data structure that allows a more agile and rapid style of development.This graph database has got its own standalone server mode, based on interaction via REST.
17. Recommendations Customers who bought P also bought {Pa, …, Pb} Customers who bought {Pa, …, Pb} also bought {Px, …, Py} Etc Popularity is a function of number of purchasers and distance from original product (products close to the original product are ranked higher than those further away)