The Third Manifesto is a proposal for relational database management systems. It was first published as a paper in 1995 by Chris Date and Hugh Darwen and further explained and expanded upon in several books by the same authors.
Date and Darwen set out the features of a relational database system by defining the features of its language and underlying type system. The original paper was a response in oposition to two earlier proposals for future database systems.
Since its publication several open-source DBMSs and at least one commercial product have been developed based on the Third Manifesto.