Well Frederic posted a good idea. The File should be some graph node.
I do HIGHLY recommend everybody to take a look at the IconKit by Scott roy. It is really well designed and perfectly fits the GraphNode stuff you have mentioned (plus ading the drag&drop stuff)
He said that he did sent a protocol def to the OPN and I guess he has nothing against dopting his interface and protocols!
This would really ease development a lot.
WE (the MiscKit) should focus on writing a good subclass of a GrapgNode (that somehow is similar to thie IKFolder or at least uses the same protocols) and can represent the File behavior. (from size to MAB infos)
File and directory could be one class (isLeaf)
We could add a default open:sender method to giv every subclass of file (TIFFFile) the chance to open itself (maybe by asking the Workspace to do that by default inside the file class)
I really enjoy this class, and I would be very glad if we could reach some kind of 'inter-kit' compatibility in this area....IconKit is very nice and I donIt wnat to have to write my own file class.