[corpMaverick]

From what I can understand (barely) The paper tries to determine if some of the new(2003) SQL3 extensions were really needed.

From the answers here https://stackoverflow.com/questions/900055/is-sql-or-even-ts...

It seems that SQL92 was not Turing complete but it became turing complete later on. Possibly by the same extensions added in SQL3.

[MarkusWinand]

The mentioned proof is confirming SQL:2003.

See also: https://wiki.postgresql.org/wiki/Cyclic_Tag_System