flex Expert System Toolkit - LPIS

6. Anatomy of a flex Program 57
The frames
The rules
The ruleset
First we define the data structures, which means declaring a frame for a
cinema and a frame for a cinema-goer. Each will have a single slot, or
attribute, which contains the number of seats for a cinema and the number
of tickets required by a viewer.
frame cinema
default seats is 500.
frame viewer
default tickets_required is 3.
We will define one rule, which describes how the cinema seats will be
allocated to the viewer. We will call this rule allocate_tickets. The
condition under which the rule will be fired is simply that the viewer requires
some tickets!
rule allocate_tickets
if the tickets_required of viewer is greater than 0
then the seats of the cinema becomes
the seats of the cinema
minus the tickets_required of viewer and
the tickets_required of viewer becomes 0.
Next, a ruleset must be defined to say what rules are to be considered.
We will call our ruleset seating; in this case we only have one rule, called
allocate_tickets.
ruleset seating
contains allocate_tickets.
The action
Finally, to set this going we invoke these rules, defining an action to do
so.
action go ;
do invoke ruleset seating.
Starting The Forward Chaining Engine
flex toolkit
We now have a complete flex program. To start the flex forward chaining
engine, we simply run the Prolog query go (type go at the Prolog command
line).
?- go.