Please, if any body can explain if is possible to use XML like model in GEF? Well, to make diagram editor in GEF then every time when load xml file to automatic populate diagrams, and after finish work to save it again in the same xml,with changes.
Well, you can defintely use XML to be the model for GEF, but your actual XML file instance cannot be a model. You will need to create your own model on the basis of the XML file. This model should have following functionalities: - way to get and set any property of the model - serialize the changes back to XML file - if possible, notification mechanism for any model changes.
All things mentioned above will not automatically happen via GEF.
Instead GEF will provide you with common functionalities like : - render your model elements as Figure`s in UI. - process user input from Mouse and keyboard. - provide hooks for updating the model - and most important, provide undo/redo support.
This answer is base upon my current level of understanding with GEF. I hope I have answered to your concerns.