The obvious question is: which concepts have to be introduced into Perl by a "RDBMS in Perl"? Which feature of RDBMs make these so attractive to be implemented in perl instead of relying on the mature solutions in this field?

Two concepts come to my mind, which would be an interesting addition to the perl datastructure zoo.

First, the idea of referential integrity, that is, declarative integrity between different objects. For example, we have a class customer, and a class bill, and the programmer can declare in advance the integrity conditions between the customer and his bills.

Second, the idea of declarative programming in general. Example: One declares a class Room and a class guest, and now, given the integrity conditions, the system generates valid "object tuples", from which one could select the most suitable that relates a guest with a corresponding room.