For several reasons, relational databases are probably the most used storage solutions by programmers and architects. There are a lot of stable tools for designing, monitoring, and querying. Both the relational model and the SQL language that are well-known among the programmers and are a part of most programming languages, such as Java, Ruby, Scala, C# and so on, have stable drivers that allow you to connect to common SQL databases. In the past, migrating from SQL could be a nightmare; your tools would stop working, and your application (or the persistence layer at least) would need to be completely rewritten. The whole reporting system could stop working as well. Nowadays, thanks to Cypher and to projects such as neo4j-jdbc, (http://www.neo4j.org/develop/tools/jdbc), the process is much simpler.

Migrating from a commercial SQL database such as SQL Server or Oracle to a graph database could happen due to several reasons: