From the conclusion of
Many questions are raised and left unanswered. ... Neither the purely
linguistic details of [the relational algebra] nor the implementation problems
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.