| The production rule system exemplified
here is slightly different from that described in your text.
It is a system that was written for use in the lab associated
with 472 which I also teach. Nonetheless, working through this
description and following the animation should give you a better
feel for how production systems work. Note particularly that
the amount of memory, the working memory, available to support
the search for a solution is quite small. And, since no tree
is maintained, the "state of the search" is maintained
in this working memory.
| The figure below illustrates the general
form of the production rules used in this example. LHS refers
to the left hand side or condition side of the rule; and, RHS
refers to the right hand side or action portion of the rules.
The form used here mirrors the form used in the lab for 830:472,
and, in fact, this software was used to generate this example.
In this form, the RHS is divided into two portions: the first
line, here shown in red, lists those expressions which are deleted
from working memory, WM, and the second line here shown in blue,
lists those expressions which are added to working memory, WM.
| The specific production rules that we
used in this example are shown in the field below. The first,
unstacks or makes a block clear if we have already established
the goal of clearing that block. The second rule intoruduces
a goal of clearing a block that is currently not clear. Note
that in this architecture we have explicitly introduced "meta"
relations; e.g. the 'goal' relation for use in controlling the
action of the production rule system.
| The next field animates the activity of
this system using these rules. The illustration includes three
components. First, in the upper right of the figure is shown
the rule that was applied on a particular cycle together with
the bindings that were found for the variables in the rule in
the match phase. Second, a depiction of the contents of working
memory (WM) is shown. In this depiction, those items shown in
darkened colors indicate items that either are not yet present
or are no longer active or relevant. Third, to the lower right
is depicted the state of the "world that corresponds to
the expressions in WM at that point.