Abstract: The B method is quite popular for developing provably correct software for safety critical railway systems, particularly for driverless trains. In recent years, the B method has also been used successfully for data validation. There, the B language has proven to be a compact way to express complex validation rules, and tools such as predicateB, Ovado or ProB can be used to provide high assurance validation engines, where a secondary toolchain validates the result of the primary toolchain.