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Codd argued this a long time ago. Unfortunately Codd died twenty years ago, so we can't ask him his current thoughts on the matter. On the other hand, Chris Dat

• goto11 4y ago
  The question isn't who said what when, the question is what reasoning holds today. Codds argument was simply that if we allow tables embedded inside fields and we want to query across multiple "layers" of embedded tables, we get a much more complex query language and implementation for no additional benefit, since the same relationship can be represented with foreign keys. I haven't seen any reasonable counterargument against this. If I understand Date correctly, he is just saying that individual values can be arbitrary complex as long as they are treated as "atomic" by the relational operators. I don't disagree, but reality is that very soon after you start storing stuff like XML or JSON in database fields, someone wants to query sub-structures, e.g. filter on individual properties in the JSON. And then you have a mess.