Continuous digitization of the world around us, and the corresponding technology penetration into our private and professional lives, is increasing the emphasis on their interoperability. Public administration, and the ongoing digitalization of their services, is no exception. This fact has long been reflected by the European Commission, and supported by several official strategies and activities. One of the concrete examples is recently published eGovernment Action Plan 2016-2020, which besides other principles, states the "interoperability by default".