Neo4j is a recent graph-database that is rapidly accumulating success stories, especially in areas such as “social applications, recommendation engines, fraud detection, resource authorization, network & data center management and much more“. Here’s an interesting introductory lecture about by Ian Robinson at JavaZone 2013.

Tip: Databasetube offers various other interesting articles about neo4j

A few notes from the presentation:

Premises: 
	- Data today is more connected than ever before
	- Complexity = f(size, semi-structure, connectedness)
	- Graphs are the best abstractions we have to model connectedness

The data model in neo4j: "property graph model"
	- nodes have properties (eg key-value pairs)
	- relationships have a direction, and can have properties too (eg weighted associations)

Neo4j server has a built in UI (web-based)

When to consider using a graph database:
	- lots of join tables [connectedness]
	- lots of sparse tables [semi-structure]

Neo4j fully supports ACID transactions
	- durable, consistent data
	- uses a try/success syntax

Performance
	- millions of 'joins' per second [connections are pre-calculated at insert time!]
	- consistent query times as dataset grows

Cypher query language
	- syntax mirrors the graphic representation of a graph 
	- one dimensional, left-to-right
	

For a comparison of various graph databases (including Neo4j) check out this tutorial from the ESWC’13 conference