Reasons why not to use Relational database?

Plain text files in a filesystem

	Very simple to create and edit

	Easy for users to manipulate with simple tools (i.e. text editors, grep etc)

	Efficient storage of binary documents



XML or JSON files on disk

	As above, but with a bit more ability to validate the structure.



Spreadsheet / CSV file

	Very easy model for business users to understand



Subversion (or similar disk based version control system)

	Very good support for versioning of data



[Berkley DB]( (Basically, a disk based hashtable)

	Very simple conceptually (just un-typed key/value)

	Quite fast

	No administration overhead

	Supports transactions I believe



[Amazon's Simple DB](

	Much like Berkley DB I believe, but hosted



[Google's App Engine Datastore](

	Hosted and highly scalable

	Per document key-value storage (i.e. flexible data model)




	Document focus

	Simple storage of semi-structured / document based data



Native language collections (stored in memory or serialised on disk)

	Very tight language integration



Custom (hand-written) storage engine

	Potentially very high performance in required uses cases