Well, I believe Rolf nailed it in identifying that "DB.pm" package as a debugger. It seems to have nothing to do with databases. In looking through its code I saw much about identifying files and nothing about tables. Most of it was so abstract as to be above my level, and the explicit parts related to debugging or error messaging had not surprised me because, well, don't all good modules have that sort of thing?

In any case, "DB.pm" is definitely not an equivalent for DBI/DBD.