Is there any tool built or any OOTB solution in Appian that generates relationsh

I guess it's not there. But a good idea for a plugin development.

That is an excellent idea. Kind of like an ERD for processes.

The closest is the Process Model Documentation which allows you to see Parent-Subprocess relationship for model A and by clicking on Subprocess A.1 you can see Parent-Subprocess relationship for subprocess A.1 if any, etc.

Thanks Eduardo, I have been using the Process Model Documentation, but it does not provide overall relationships among Process Models in a bird's-eye view. something like an ERD would be helpful in understanding the realtionships between process model, mainly helpful to new designers in the project in comprehending the architecture/relationships.

I have managed to extract all the process models and their relationships from XML files.

Then I used a data modelling tool (Gephi) to visualize the relationships. The result was not satisfactory. See attached.

It is something to start with. Thanks Mobin for pointing out the tool.