Data Modeling vs. Database Design

01 Dec 96 updated

RDBMS Products
vs. Relational Theory

 Each vendor competing in the RDBMS features war vies to differentiate its product with speed, reliability, and ease of use. Vendors also add extensions beyond basic relational theory, all of which are useful, some of which are problematic.

For example, indexes are clearly non-relational, in the strictest sense. The essence of a relation is lack of physical order or position. Yet an index holds ordered values with pointers to physical locations. Obviously, indexes are a valuable, and universal, extension to basic relational theory.

Note below that for technical and historical reasons, RDBMS practice abandons the arcane terms of set mathematics. So in the database we call a relation a table and a tuple becomes a row, etc.

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