So what is the meaning of "atomic"? Are array-typed values atomic? (I think you can treat it that way, a lot of lists are immutable in different programming languages.)
> But he betrays very little knowledge of the relational model.
This is absolutely possible. Let me ask a couple of questions to borrow from your understanding of relational model.
> Repeating fields, which he proclaims as some kind of innovation, violate 1NF. They’re not atomic.
Sorry, what is "repeating fields"? I don't remember ever using this, how does it look like? Are you talking about array-typed columns? If yes, then why are they not atomic?
Also, I don't think I proclaim absolutely anything is "kind of innovation"? Postgresql supports array-typed columns since 2001, and it was planned in 1986 already as part of other "post-relational" features.
Two schemas "(instructor_id, List<skill_id>); PK(instructor_id)", and "(instructor_id, skill_id); PK(instructor_id, skill_id)" are isomorphic, thus I may be wrong but I don't see any anomalies here.
> Maybe the easiest way to understand it is that the list of languages can’t be used in SQL. If one teacher speaks Italian and French, SQL won’t find WHERE LANGUAGE = ‘FRENCH’.
Ah, so you seem to be talking about array-typed columns. I mean, you can find it easily by using "WHERE languages @> ARRAY['FRENCH']". The difference is mostly syntactical.
If you think that you are not allowed to access single elements of "languages" array because it violates "atomicity" of the value, then we should also say that you're not allowed to use queries like "WHERE name LIKE 'A%'", because they violate the atomicity of a string value. Don't you agree?
> SQL doesn’t recognize repeating fields in a column
Array-typed columns appeared in ANSI SQL:1999, a quarter of century ago. I'm not sure what you're talking about.