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	$self->_add_to_log( "${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 
to consult the example knowledge bases and more extensive documemtation in the docs directory.

There is a Ruby version that reads the same XML knowledge bases, if you are interested.

=head2 Constructors and initialisation

=over 4

=item new( )

The constructor takes no arguments and just initialises a few basic variables.

=back

=head2 Public methods

=over 4

=item reset( )

Resets the system back to its initial state so that a new consoltation can be run

=item load( FILENAME )

This method takes the FILENAME of an XML knowledgebase and attempts to parse it to set up the data structures 
required for a consoltation.

=item process( )

Once the knowledgebase is loaded the consultation is run by repeatedly calling this method.

It returns four results:

=over 4

=item "question"

The system has a question to ask of the user.

The question and list of valid responses is available from the get_question( ) method and the users response should be returned via the answer( ) method. 

Then simply call the process( ) method again.

=item "continue"

The system has calculated some data but has nothing to ask the user but has still not finished.

This response will be removed in future versions.

Simply call the process( ) method again.

=item "finished"

The consoltation has finished and the system has an answer for the user which is available from the answer( ) method.

=item "failed"

The consoltation has finished and the system has failed to find an answer for the user. It happens.