<https://codesteps.com/2014/07/26/ruby-programming-an-overview-on-classes/#breadcrumb>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://schema.org/BreadcrumbList>
<https://codesteps.com/2014/07/26/ruby-programming-an-overview-on-classes/>