[layer8]

I mostly agree with you, however one could argue that character strings aren’t atomic as well. They are sequences (“arrays”, if you will) of characters, and query operators like LIKE demonstrate that strings aren’t just used as opaque values. You could in principle normalize character strings into a String table with columns “string ID”, “character position”, and “character value”. Somewhat similarly, types like DATETIME and INTERVAL can be regarded as non-atomic.

Whether a database column has a composite type is a trade-off regarding performance, storage requirements, and needing special operators for queries to work on the substructure of a composite value.