Like BPMN, Eclipse Free BIRD Tools provides a notation for visualizing its models, and also a text means for storing instances of the models.
Previoulsy we have used XMI or XML following an XMLSchema (these are alos the 2 options provided by BPMN), however we have decided that JSON is a better text format for this purpose.
JSON in our view is easier to read if you need to read it, and easier to compare between versions.
We dont consider that users should ever need to look at the JSON directly (just like users of BPMN never look at the text storage of the file), as the project aims to provide visual rendering, and simple visual builders using drag and drop and property views for all models.