my %_attribute_properties = (
		
 _probeset_id        => ['????',   'read.required'],  
...
_affy_align         => [ ['????'] ,    'read.write.noinit'   ]
_exons_map          => [ { }       ,   'read.write.noinit'   ]
...

);

##</code><code>##


# AUTOLOAD Accesors
	if ($operation eq 'get') {
		# can i read the attribute?
		unless ($self -> _permissions ($attribute, 'read')) {
			die ("You don't have read permission for $attribute");
		}
		
		#
		# Install accessor definition in the symbol table
		# How AUTOLOAD work: *{$VAR} give access to the symbol definition table so, 
		# the second time that the method get_name is called AUTOLOAD isn't called cause
		# get_name is saved in the symbol table
		
		*{$AUTOLOAD} = sub {
			my ($self) = @_;
			unless ($self -> _permissions($attribute, 'read')) {
				die ("$attribute does not have read permission!");
			}
			# get the attribute value
			# TIE-HASH da inserire qui
			# The attribute could be a scalar or a reference to an array or hash
			if (ref($self -> {$attribute}) eq 'ARRAY') {
				return @{$self->{$attribute}};
			} elsif (ref($self -> {$attribute}) eq 'HASH') {
				return %{$self->{$attribute}};
			} else {
				return $self -> {$attribute};
			}
		}; 
		
		
	}elsif ($operation eq 'set') {
		# Verify if you can set the attribute
		unless ($self -> _permissions($attribute, 'write')) {
			die ("$attribute does not have write permission!");
		}
		# set the attribute value
		$self -> {$attribute} = $newvalue;
		
		# Install this mutator in the symbol table
		*{$AUTOLOAD} = sub {
			my ($self, $newvalue) = @_;
			unless ($self -> _permissions($attribute, 'write')) {
				die ("$attribute does not have write permission!");
			}
			$self -> {$attribute} = $newvalue;
		};
	}
	# Turn strict refs on
	use strict  'refs';
	# Return the attribute value
	return $self -> {$attribute};
}

# }}}