Any declarative language that does not commit the violations of the relational model that SQL does commit. Date&Darwen formally pinned down what such a languag

Any declarative language that does not commit the violations of the relational model that SQL does commit. Date&Darwen formally pinned down what such a language has to look like in their three subsequent editions of "the third manifesto" (first edition roundabouts 1995). There are at least two fully operational systems that comply.