12.2. Relational Database Systems
We may now define a relational DBMS as a DBMS that has the relational table as its only essential data structure and supports the selection, projection, and join operations without needing specification of physical access paths. A relational system that supports all eight table operations of the relational algebra is said to be relationally complete. This doesn’t entail eight distinct operators for these tasks; rather, the eight operations must be expressible in terms of the table operations provided by the system.
The two main relational languages are SQL and QBE, with SQL being the most important. Most SQL systems are relationally complete. A system that supports all aspects of the relational model, including ...
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