Drivers and Barriers for OOP (1st version) : The Once-Only Principle Project [Online resource]Kalvet, Tarmo; Toots, Maarja; Krimmer, Robert Johannes2017 http://toop.eu/sites/default/files/D27_Drivers_and_Barriers.pdf

Position paper on definition of OOP and situation in Europe : The Once-Only Principle Project [Online resource]Krimmer, Robert Johannes; Kalvet, Tarmo; Toots, Maarja; Cepilovs, Aleksandrs2017 http://toop.eu/sites/default/files/D2.6_Position_Paper_OOP.pdf