It's nonsense. The author arbitrarily decides on some expression of the windowing model in terms of files. OK cool. Every author of a system that uses files decides how to represent their data. E.g. how many files to use, sockets, what data to flow through each and what format that data should be represented in. Like why not go to the authors of Btrfs and argue why the data format /dev/btrfs-control is the way it is why it's a single file instead of 5. It's an arbitrary decision. When not used for storing data files in POSIX-like OSes are a type of IPC mechanism. How many channels that IPC needs and what data flows over these channels is an arbitrary decision by the authors on one or both sides of that IPC. The OS provides the IPC mechanism. The software that uses it creates some abstraction on top of it which doesn't have to conform to any lower level OS models. Could we model Postgres tables and rows like files in a dir structure. Sure. There are pros and cons to using that model. Might not be great for terabyte scale db performance.