The precise definition of Model D
logical and physical operators
is somewhat arbitrary.
Part of the reason for this is the
experimental nature of Model D.
different approaches were available,
to try each one
to see the
ramifications of the different strategies.
The rules set consists of
their conditions for firing
and how the consequent expressions are constructed.
describes what information
each stored relation and all defined indices
is required in order calculate
logical properties and evaluate rule conditions.