Traditional enterprize systems have well developed designs & strategies around relational databases. Relational database products are well developed not only from a data consistency point of view (ACID) but also from a database administration perspective. Databases are maintained in house or sourced to a competent vendor who has a well developed process for backup, migration and security. In contrast to this, the emerging cloud technologies employ NO SQL database structure more often than not.
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Google App Engine: Database Strategies