http://www.mcjones.org/System_R/SQL_Reunion_95/sqlr95-Prehisto.html

Quote reference: strange_math

"...We knew sort of peripherally that there was some [database research] going on in the provinces, in San Jose. There was this guy '''Ted Codd''' who had '''some kind of strange mathematical notation, but nobody took it very seriously'''. Ray Boyce was hired at about this time, and we kind of got into this game called the Query Game where we were thinking of ways to express complicated queries. But actually before the Query Game started, I had a '''conversion experience''', and I still remember this. Ted Codd came to visit Yorktown, I think it might have been at this symposium that Irv alluded to. He gave a seminar and a lot of us went to listen to him. This was as I say a revelation for me because Codd had a bunch of [sample] queries that were fairly complicated queries and since I'd been studying '''CODASYL, I could imagine how those queries would have been represented in CODASYL by programs that were five pages long that would navigate through this labyrinth of pointers and stuff'''. Codd would sort of '''write them down as one-liners'''. These would be queries like, "Find the employees who earn more than their managers." {laughter} He just whacked them out and '''you could sort of read them, and they weren't complicated at all, and I said, "Wow."''' This was kind of a conversion experience for me, that I understood what the relational thing was about after that." (Don Chamberlin, emphasis added)

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Another interesting infamous history lesson on relational is how Ed Codd came up with the name "relational" and "foreign keys".  It's somewhere on the internet but the story goes like this: He had his radio or tv on, and he heard them talking about foreign affairs or "foreign relations" with international countries on the news (some kind of peace or war or international trading discussion).  He got the idea from this that data relates, and that there are foreign things to keep track of. This seems quite informal and non mathematical.. where he got the name from... it's almost a metaphor/analogy. However he added the math and rigor, AnameIsJustaName so it doesn't matter all that much. If it was called something else, it would still be proven useful.