text: define(['knockout'], function (ko) {
  	var debug = false;
  
  	function Period(data) {
  		var self = this;
  		data = data || {};
  
  		self.StartDate = ko.observable(data.StartDate === 0 ? 0 : data.StartDate || null);
  		self.EndDate = ko.observable(data.EndDate === 0 ? 0 : data.EndDate || null);
  	}
  
  	Period.prototype.toJSON = function () {
  		return {
  			StartDate : this.StartDate instanceof Date ? (this.StartDate.toISOString().slice(0,10)) : this.StartDate,
  			EndDate: this.EndDate instanceof Date ? (this.EndDate.toISOString().slice(0,10)) : this.EndDate
  		}
  	}
  	
  	return Period;
  });