Domagoj Madunic's List: Programming Tips and ticks

Relational databases have ruled data storage for more than 30 years, but the growing  popularity of schemaless (or NoSQL) databases suggests that change is underway. While the RDBMS provides a rock-solid foundation for storing data in traditional client-server architectures, it doesn't easily (or cheaply) scale to multiple nodes. In the era of highly scalable Web apps like Facebook and Twitter, that's a very unfortunate weakness to have.

Non-relational datastores don't have join tables or primary keys, or even the notion of foreign keys (although keys of both types are present in a looser form).