Do you have some examples of how tables are "synonymous with CT itself"?
There may be some application of concepts from category theory to relational algebra, of course, since category theory is incredibly abstract and has some tangential relation with most everything. But it seems a bit too glib to say that tables are "synonymous with CT itself".
I was intrigued by that statement as well and it sent me off on a little research excursion.
Evidently a mathematician at MIT, David Spivak[0], has done some work on Databases as Categories. I found a presentation he gave to Galois[1] and a summary of the talk by E.Z. Yang.[2].
That said, I think "tables synonymous with CT itself" is a bit strong. Rather, the argument is that database schemas are categories if you model it appropriately: tables are objects in the category, and foreign keys are the morphisms/arrows).
There may be some application of concepts from category theory to relational algebra, of course, since category theory is incredibly abstract and has some tangential relation with most everything. But it seems a bit too glib to say that tables are "synonymous with CT itself".