One of the key priorities of every state is to achieve the interoperability of all key state's information systems. In the first line, this ambitious process requires establishing of new legislative measures and the follow-up adjustment of existing but not fully sound law, ensuring the technical character and harmonising the semantic side of document structures. In the first phase of this complicated process the priority is to harmonise key information systems - registers, which are inevitable for implementing electronic public administration. Subsequently, smaller units and databases will be design to achieve the full interoperability, when all these systems will be mutual connected to exchange data without any other complicated procedures. The result of this process will be accessibility and sharing of data of all linked systems in accordance with needs of their users either of public administration or business sector.