 Rovelli and coworkers have also proposed a relational interpretation of quantum mechanics in which there is the possibility of different perspective-dependent descriptions of a physical system (Rovelli 1996, Rovelli and Smerlak 2007, Laudisa and Rovelli 2021, see also van Fraassen 2010 and the entry  relational quantum mechanics.)  There are points of contact between PMI and Rovelli’s relational interpretation, but also differences. In Rovelli’s proposal, discrete interaction events (some of which correspond to measurements) are fundamental and the state has to be updated every time such an interaction event occurs. By contrast, in PMI the state evolution is always unitary.