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	my ($self, $value) = @_;

	die "Simple->answer() takes 1 argument" if scalar(@_) != 2;
	die "Simple->answer() argument 1 (VALUE) is undefined" if ! defined($value);

	$self->{_told_about} = $value;
}

sub get_answer {
	my ($self) = @_;

	die "Simple->get_answer() takes no arguments" if scalar(@_) != 1;

	my $n = $self->{_goal}->name();

	return $self->{_goal}->answer($self->{_knowledge}->{$n}->get_value());
}

sub log {
	my ($self) = @_;

	die "Simple->log() takes no arguments" if scalar(@_) != 1;

	my @return = ();
	@return = @{$self->{_log}} if defined @{$self->{_log}};

	$self->{_log} = ();

	return @return;
}

sub _add_to_log {
	my ($self, $message) = @_;

	push( @{$self->{_log}}, $message );
}

sub explain {
	my ($self) = @_;

	die "Simple->explain() takes no arguments" if scalar(@_) != 1;

	my $name  = $self->{_goal}->name();
	my $rule  = $self->{_knowledge}->{$name}->get_setter();
	my $value = $self->{_knowledge}->{$name}->get_value();

	my $x = "The goal '$name' was set to '$value' by " . ($rule ? "rule '$rule'" : 'asking a question' );
	$self->_add_to_log( $x );

	my @processed_rules;
	push( @processed_rules, $rule ) if $rule;

	$self->_explain_this( $rule, '', @processed_rules );
}

sub _explain_this {
	my ($self, $rule, $depth, @processed_rules) = @_;

	$self->_add_to_log( "${depth}Explaining rule '$rule'" );

	my %dont_do_these = map{ $_ => 1 } @processed_rules;

	my @check_these_rules = ();

	my %conditions = $self->{_rules}->{$rule}->conditions();
	foreach my $name (sort keys %conditions) {
		my $value = $conditions{$name};
		my $setter = $self->{_knowledge}->{$name}->get_setter();

		my $x = "$depth Condition '$name' was set to '$value' by " . ($setter ? "rule '$setter'" : 'asking a question' );
		$self->_add_to_log( $x );

		if($setter) {
			unless($dont_do_these{$setter}) {
				$dont_do_these{$setter} = 1;
				push( @check_these_rules, $setter );
			}
		}
	}

	my %actions = $self->{_rules}->{$rule}->actions();
	foreach my $name (sort keys %actions) {
		my $value = $actions{$name};

		my $x = "$depth Action set '$name' to '$value'";
		$self->_add_to_log( $x );
	}

	@processed_rules = keys %dont_do_these;

	foreach my $x ( @check_these_rules ) {
		push( @processed_rules, $self->_explain_this( $x, "$depth ", keys %dont_do_these ) );
	}

	return @processed_rules;
}

1;

=head1 NAME

AI::ExpertSystem::Simple - A simple expert system shell

=head1 VERSION

This document refers to verion 1.2 of AI::ExpertSystem::Simple, released June 10, 2003

=head1 SYNOPSIS

This class implements a simple expert system shell that reads the rules from an XML 
knowledge base and questions the user as it attempts to arrive at a conclusion.

=head1 DESCRIPTION

=head2 Overview

This class is where all the work is being done and the other three classes are only 
there for support. At present there is little you can do with it other than run it. Future 
version will make subclassing of this class feasable and features like logging will be introduced.

To see how to use this class there is a simple shell in the bin directory which allows you