What is the difference between a symbol and a SymbolModel?

A symbol is a node in a diagram that has child nodes and that can have ports and labels. Symbols are what the end-user typically manipulates on a diagram. A SymbolModel is an object that contains design-time information describing a type of symbol. The Symbol Designer utility creates and edits symbol models, which it stores in a SymbolPalette. SymbolModels can also be created programatically.

A SymbolPalette is a collection of SymbolModel objects. The SymbolModel class has a CreateInstance() method for creating symbols based on the model.

The PaletteGroupView control displays a list of the SymbolModel objects in a given SymbolPalette. Each time you start dragging an entry from the list in a PaletteGroupView, SymbolModel.CreateInstance() is called to create an instance of the symbol.