Germany is a federal, parliamentary, representative democratic republic. Federal legislative power is vested in the parliament consisting of the  (Federal Diet) and  (Federal Council), which together form the legislative body. The  is elected through direct elections using the mixed-member proportional representation system. The members of the  represent and are appointed by the governments of the sixteen federated states. The German political system operates under a framework laid out in the 1949 constitution known as the  (Basic Law). Amendments generally require a two-thirds majority of both the  and the ; the fundamental principles of the constitution, as expressed in the articles guaranteeing human dignity, the separation of powers, the federal structure, and the rule of law, are valid in perpetuity.