You seem to be asking this question in a vacuum, which makes it impossible to address the costs and benefits of relational vs. alternative approaches with any c

You seem to be asking this question in a vacuum, which makes it impossible to address the costs and benefits of relational vs. alternative approaches with any context. What types of problem are you trying to solve? What alternatives to an RDBMS are you proposing to solve them with? Having said that, I write transactional business applications (often dismissively referred to as "CRUD Apps), and in that context an RDBMS is a sensible default, but not for every part - so on Google App Engine for example I'm using CloudSQL for the business data, but Google's data store for the session data - because that has very different characteristics. [1] I'm reading "SQL" as shorthand for relational, although the two are hardly synonymous.