Caballero Roldán, RafaelStuckey, Peter J.Tenorio Fornés, Ámbar2023-06-182023-06-182015-11-010167-642310.1016/j.scico.2015.04.007https://hdl.handle.net/20.500.14352/24376In this paper we present two type extensions for the modelling language MiniZinc that allow the representation of some problems in a more natural way. The first proposal, called MiniZinc? , extends existing types with additional values. The user can specify both the extension of a predefined type with new values, and the behavior of the operations with relation to the new types. We illustrate the usage of MiniZinc? to model SQL-like problems with integer variables extended with NULL values. The second extension, MiniZinc+, introduces union types in the language. This allows defining recursive types such as trees, which are very useful for modelling problems that involve complex structures. A new case statement is introduced to select the different components of union type terms. The paper shows how a model defined using these extensions can be transformed into a MiniZinc model which is equivalent to the original model.engjournal articlehttp://dx.doi.org/10.1016/j.scico.2015.04.007open access004.438MiniZincConstraint ProgrammingNULL valuesUnion TypesLenguajes de programación1203.23 Lenguajes de Programación