In the same 1971 seminar where we studied Algol-68, we had to read and write a short paper on the 1970 Codd paper on relational theory, which had only been out for about a year. The professor running the seminar noted that Codd proved that the relational model worked, but didn't guarantee that it worked efficiently enough to be implementable without immense computer resources, which of course became available.
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Mike Nolan