Referential integrity with Scala types

Referential integrity constraints are critical elements of relational data models, and have found widespread use in industry. However, their benefits in terms of data integrity do not fully extend to program correctness. Constraint violations are identified at run-time and must then be handled appropriately by programs. We show how Scala can be used to build data models and programs where referential integrity is enforced at compile-time. Scala’s type system, with its variance annotations and path-dependent types, is especially suited to express these constraints and proofs in a natural manner. We also explore potential compiler improvements that could enhance support for type-checked referential integrity.