The Codd 1971 stuff on Wikipedia looks like a mess, and I think the original is propbably a bit crufty too (though I don't want to disrespect the old masters, SQL was a high water mark of business thinking about computing in many ways).

I would follow the citations of https://ncatlab.org/nlab/show/lens+%28in+computer+science%29 instead. Whatever Spivack can say about this stuff I think is going to be much more worth your while.

Looking at https://arxiv.org/pdf/1602.03501.pdf now.