[From CNET News
"Database" has come to be largely synonymous with a relational database management system (RDBMS) or, more specifically, a relational database that is accessed using the SQL query language. Some simpler products run on desktops, but if you are talking about products used for serious business computing on a server, SQL it is. The widespread adoption of open-source products such as MySQL and PostgreSQL only cemented SQL's dominance by making it available to a broad audience that couldn't afford licensing fees for products from Oracle and other large database vendors.
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