LISP provides for every symbol a property list that associates named properties with the symbol:

             binding
PRESIDENT --------->   BUSH
  |                     |
  | DUTIES (CINC ...)   | WIFE ----->  LAURA
  |                     |               |
  | ...                 | AGE  58       |

This mechanism has several advantages:

1. New properties can be added at any time; there is no need to pre-declare properties.

2. Only those properties needed for each individual object need to be stored.

3. A property can have a single value or a list of values associated with it.

Property lists are a natural mechanism to use in implementing semantic networks.

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