$namedHash { unique field value across both records } = {

	legacy_system => {
	
		'goodField' => 'I am good!',
		'firstField' => 1,
		'secondField' => 3
	},

	new_system => {
	
		'firstField' => 11,
		'secondField' => 33,
		'goodField' => 'I am good!'
	},

	differences => [firstField, secondField];
};