Type inference in the polymorphic relational algebra
Jan Van den Bussche, Emmanuel Waller · 1999
We give a polymorphic account of the relational algebra.We introduce a formalism of "type formulas" specifically tuned for relational algebra expressions, and present an algorithm that computes the ".principal" type for a given expression.The principal type ojF an expression is a formula that specifies, in a clear and concise manner, all assignments of types (sets of attributes) tO relation names, under which a given relational algebra expression is well-typed, as well as the output type that expression will have under each of these assignments.Topics discussed include complexity, the relationship with monadic logic, and polymorphic expressive power.