Is there any documentation regarding the relationship between eisy, IoX, and PG3?

The UDI Wiki is your best source

https://wiki.universal-devices.com/Main_Page#Online_Documentation

If you're looking for something specific then the forum would also be a good choice.

This is exactly what I have suspected-There is NO documentation on how the entire framework ties together. For example PG3 runs partially on the eisy, but is also must have a central database somewhere in order to keep track of licenses and plugin info. Where is all of this because it it too big to reside totally on the eisy (there are other good reasons why PG3 can't totally run on the eisy)?

What I am looking for is a layout of how the entire framework ties together. You can call it the system architecture, but that is exactly what I am looking for. I have asked Michel for this, and he has ignored me. I thought perhaps someone in the forum could enlighten me.

Well we can sort of deduce some things after using it for a while. If you compare the system to a Windows application you create that's running on a Windows PC (a Visual Basic program for example) you'll see that there are many system calls and resources that allow your applications to hook into the operating system. File access, mouse movements and actions, writing on the screen, network events, etc. The eisy runs on unix and multitasking has always existed on unix, long before DOS was even created. There are various methods of interprocess communications built into unix (like when you fork a new process, it inherits all the file descriptors of the parent process) though nowadays interprocess communications is often done through sockets. So an add on like PGx will often access an application programming interface (API) that's defined just like system calls are made available to Windows processes. The various IoX resources are defined as API calls that your program (plugin) can use to exchange information to and from IoX. Defined objects (nodes), programs, and variables would be stored in a database, which allows external applications such as eisy-ui to retrieve them. Editors like admin console (and soon, eisy-ui) can also modify the database.

Just some thoughts.