ACM Queue - Beyond Relational Databases - There is more to data access than SQL.

"As soon as the discussion turns to data storage and retrieval, relational databases come to mind. Relational databases have been tremendously successful over the past three decades, and SQL has become the lingua franca for data access. While data management has become almost synonymous with RDBMS, however, there are an increasing number of applications for which lighter-weight alternatives are more appropriate."