Amazon SimpleDB is a highly available, flexible, and scalable non-relational data store that offloads the work of database administration.
Developers simply store and query data items via web services requests, and Amazon SimpleDB does the rest.
Unbound by the strict requirements of a relational database, Amazon SimpleDB is optimized to provide high availability, flexibility, and ease of scalability with little or no administrative burden.
Behind the scenes, Amazon SimpleDB creates and manages multiple geographically distributed replicas of your data automatically to enable high availability and data durability. The service charges you only for the resources actually consumed in storing your data and serving your requests. You can change your data model on the fly, and data is automatically indexed for you.
With Amazon SimpleDB, you can focus on application development without worrying about infrastructure provisioning, high availability, software maintenance, schema and index management, or performance tuning.