In his seminal paper A Relational Model of Data for Large Shared Data Banks, Codd explicitly mentions first-order predicate calculus as a suitable formalism for

In his seminal paper A Relational Model of Data for Large Shared Data Banks, Codd explicitly mentions first-order predicate calculus as a suitable formalism for the sub-language. Quoting from https://dl.acm.org/doi/pdf/10.1145/362384.362685 https://dl.acm.org/doi/pdf/10.1145/362384.362685: "The adoption of a relational model of data, as described above, permits the development of a universal data sub-language based on an applied predicate calculus. A first-order predicate calculus suffices if the collection of relationships is in normal form." One great advantage of using Prolog is that queries themselves are so readily amenable to analysis and reasoning with the same mechanism, and it becomes very easy to optimize them by reordering goals.