: A Peer-to-peer Data Network (PDN) is an open and evolving society of peer nodes that assemble into a network to share their data for mutual benefit. PDNs are enabled by distributed query processing. We argue that with a self-organizing, dynamic, and large-scale architecture and nodes that inherit extensive autonomy from their human users, this new generation of distributed database systems should be upgraded from the domain of traditional distributed computing systems to the realm of natural complex systems (such as social networks). In this way, PDN is studied among its peers within a modelling framework which is both compatible with its natural/autonomous computing model and rich to capture its complexity. The “complex system theory” is a meta-theory that provides a common modelling framework to study such complex systems under one umbrella. This meta-theory consists of a rich collection of tools adopted from various fields, where each tool is developed to study an instance o...