The Third Manifesto by Darwen and Date (1995, 2000) attempts to defend the relational
data model as described in the authors’ 1992 book (Date and Darwen, 1992). It is
acknowledged that certain object-oriented features are desirable, but the authors believe
these features to be orthogonal to the relational model, so that ‘the relational model needsno extension, no correction, no subsumption, and, above all, no perversion’. However,
SQL is unequivocally rejected as a perversion of the model and instead a language called
D is proposed. Instead, it is suggested that a frontend layer is furnished to D that allows
SQL to be used, thus providing a migration path for existing SQL users. The manifesto
proposes that D be subject to: