Angela Dappert et al. have published "Connecting the Persistent Identifier Ecosystem: Building the Technical and Human Infrastructure for Open Research" in the Data Science Journal.
Here's an excerpt:
This article draws on the work of the EU-funded THOR project to take stock of the current state of interoperability across the PID landscape and to discuss the next steps towards an integrated research record. Examples illustrate how this interconnectivity is facilitated technically, as well as social and human challenges in fostering adoption. User stories highlight how this network of persistent identifier services is facilitating good practice in open research and where its limitations lie.