>That is pretty clearly contrary to the basics of the relational model itself
The consensus among relational theorists appears to be that data types can be arbitrarily complex. For instance, C.J Date and Hugh Darwen write the following ([1] page 56):
Third, we remind you that types are not limited to simple things like integers. Indeed, we saw in Chapter 1 that values and variables can be arbitrarily complex—and that is so precisely because the types of those values and variables can be arbitrarily complex. Thus, to paraphrase a remark from that chapter, a type might consist of geometric points, or polygons, or X rays, or XML documents, or fingerprints, or arrays, or stacks, or lists, or relations (and on and on).
The consensus among relational theorists appears to be that data types can be arbitrarily complex. For instance, C.J Date and Hugh Darwen write the following ([1] page 56):
Third, we remind you that types are not limited to simple things like integers. Indeed, we saw in Chapter 1 that values and variables can be arbitrarily complex—and that is so precisely because the types of those values and variables can be arbitrarily complex. Thus, to paraphrase a remark from that chapter, a type might consist of geometric points, or polygons, or X rays, or XML documents, or fingerprints, or arrays, or stacks, or lists, or relations (and on and on).
[1] https://www.dcs.warwick.ac.uk/~hugh/TTM/DTATRM.pdf