Graphs : Relational database versus Graph database

Check the following articles on how to represent graphs in both a relational database and graph database:

 

Graphs in the database: SQL meets social networks

http://techportal.ibuildings.com/2009/09/07/graphs-in-the-database-sql-meets-social-networks/

Social networks in the database: using a graph database

http://blog.neo4j.org/2009/09/social-networks-in-database-using-graph.html