Yesterday I found the ordered list of data block references. So I can extract the name of every data block. There must be a tree underneath the data block structure, which contains the references to the item objects. This point I still have to find out.

In the meantime, the output of the decompiler is already very huge, so I should write a graphical representation of the content, like FormBuilder Object Navigator. A simple approach to JavaFX and MVC you can find here.