The compare of two (versions) or SmartFramework ERD models (.smfdia files) or Progress .df files is implemented based on the standard "Compare with each other" tool in the Project Explorer context menu. It also works with Eclipse team providers using the "Compare with revision" menus.
It is possible to compare a diagram with a data definition. But the output may be "polluted" by reference changes.
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The easiest way to create in incremental data definition file (delta.df) are the wizards that can be reached from the context menu of the model design canvas:
