In common D/S relationships the submissive may only submit occasionally and with definite short-term goals, perhaps for an evening or the duration of a party. In longer, committed relationships many people opt for a Master/slave or Mistress/slave model, in which consent is negotiated once for a long period and the consent given is generally broader. Some people opt to be purely “sex slaves”, while others who prefer domestic service identify as “service slaves”. Some slaves allow their Masters or Mistresses complete latitude as to the demands that can be placed on them. Such a relationship is known as “Total Power Exchange” or TPE).