A frame can represent an individual object or a class of similar objects.

Instead of properties, a frame has slots. A slot is like a property, but can contain more kinds of information (sometimes called facets of the slot):

• The value of the slot; default value in case no value is present.

• A procedure that can be run to compute the value (an if-needed procedure).

• Procedures to be run when a value is put into the slot or removed ( if-added and if-removed procedures). These can be used to implement demons.

• Data type information; constraints on possible slot fillers.

• Documentation.

Frames can inherit slots from parent frames. For example, FIDO (an individual dog) might inherit properties from DOG (its parent class) or MAMMAL (a parent class of DOG).

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