OPS5 and Mercury are examples of fifth-generation languages,[2] as is ICAD, which was built upon Lisp.
In the 1980s, fifth-generation languages were considered to be the way of the future, and some predicted that they would replace procedural programming with constraint based programming for all tasks that could be framed as a series of logical constraints.
This crucial step cannot yet be automated and still requires the insight of a human programmer.
Most of the time they actually sell 4GLs with a higher level of automation and knowledge base.
Because the hype of the 1980s faded away and the projects were eventually all dropped, 5GL awareness has also dropped; this has opened doors to the vendors to reuse the term in marketing their new tools, without causing much controversy among the current generations of programmers.