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Relational Algebra

From the conclusion of Codd's paper:

Many questions are raised and left unanswered. ... Neither the purely linguistic details of [the relational algebra] nor the implementation problems are discussed. Nevertheless, the material presented should be adequate for experienced systems programmers to visualize several approaches.

  • The Relational Model is far more abstract than contemporary models (hierarchical, network).

  • All three models map to storage in obvious ways.

  • But the hierarchical and network languages and APIs are low-level, and therefore easily, obviously implementable.

  • The relational algebra is a much bigger step.

  • But still imaginable.

  • What followed was 10 years of research and development before the first barely usable relational database systems were available.

  • Another 10 years before they were widely accepted.

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