Frame systems typically have the following features in contrast to typical object-oriented systems:

• Richer slots. A slot can contain more kinds of information, e.g., documentation, default value, restrictions on slot fillers, if-added and if-removed methods.

• Slot orientation. There usually are no ``messages'' that are not associated with slots.

• More complex structure. A frame system could potentially have instance values, default values, and if-needed methods for the same slot. When all these are combined with multiple inheritance paths, the result can be complex.

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