The topicality of the thesis is given by the new interoperability provisions of the recently enacted legislation on contestable and fair markets. In interpreting the role of interoperability, the study takes as a conceptual starting point the ability of different IT-based systems to work together, bearing in mind that in digital markets interoperability is a direct economic determinant of interoperability between platforms and third-party access. Gatekeepers as digital platforms have become a dominant phenomenon in our world, which may be extremely heterogeneous, but almost without exception they can be identified as having a number of interdependent technological, economic and social dimensions of coordination. It is true that the last few decades have seen the recurrence of legal issues relating to the management of data, but these are primarily constitutional approaches in the context of the individual's right to self-determination. Furthermore, it is a fact that enforcement and regulation have not kept pace with the development of extreme market concentration, nor with the achievement of transparency or accountability. The thesis takes a novel approach in several respects. On the one hand, it takes a power approach to the new world of digital sovereignty that has emerged in the last decade, and on the other hand, it uses the latest findings in systems theory and data science to present a specific approach that, in the current state of technological development, self-determination is no longer necessarily adequate to protect our data. We all have to come to grips with the idea that our data, traces of our behaviour, have become an asset that may be being processed and analysed by someone, somewhere. That does not make privacy 'dead' as many people think - it is simply that the focus may be on the rules for handling personal data rather than protecting it.