Sql 不使用关系数据库的充分理由

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

Berkeley 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 Berkeley DB I believe, but hosted

Google's App Engine Datastore

• Hosted and highly scalable
• Per document key-value storage (i.e. flexible data model)

CouchDB

• 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

I can't claim to know anything much about them, but you might also like to look into object database systems.