Entityeither

Entityeither is a modeling construct used in knowledge representation and data modeling to describe a value or reference that may point to one of two alternative entities. It captures a disjunctive type, akin to a sum type or discriminated union, in which a given instance belongs to exactly one of the two alternatives, or in some cases to at least one if inclusive. In practice, entityeither is represented by a union or choice of two candidate entities, with constraints added to guide how the choice is determined.

In ontology languages and schema design, entityeither can be implemented by combining the two candidate classes and applying constraints to express the intended exclusivity or inclusivity. For example, in OWL, an entityeither between Person and Organization can be modeled using a class that is the unionOf(Person, Organization). To enforce that an instance is associated with a single alternative, disjointness axioms between Person and Organization are used, unless the system allows the possibility of both.

Example usage: a contactableEntity field might be modeled as entityeither(Person, Organization). A value would be a Person instance or an Organization instance, with a type tag or constraints ensuring a valid choice. In programming and data modeling, this mirrors discriminated unions or algebraic data types, providing a clear and type-safe way to represent polymorphic references.

Applications include data integration, schema evolution, and polymorphic relationships in knowledge bases. Not all systems implement a dedicated keyword for entityeither, but the pattern aligns with existing concepts such as union classes, sum types, and discriminated unions.