constructor(material: Material, task: Task) {
   ValidatableMixin.call(this);
   this.material = stream(material);
   this.task     = stream(task);
   this.validateAssociated("material");
   this.validateAssociated("task");
 }

 protected constructor(name: string,
                       autoUpdate: boolean,
                       errors: { [key: string]: string[] } = {}) {
   super();
   this.name       = stream(name);
   this.autoUpdate = stream(autoUpdate);
   ValidatableMixin.call(this);
   this.errors(new Errors(errors));
 }

 constructor(directive: string, action: string, type: string, resource: string) {
   super();
   ValidatableMixin.call(this);
   this.directive = stream(directive);
   this.action    = stream(action);
   this.type      = stream(type);
   this.resource  = stream(resource);
   this.validatePresenceOf("directive");
   this.validatePresenceOf("action");
   this.validatePresenceOf("type");
 }

  constructor(id?: string, pluginId?: string, properties?: Configurations) {
    this.id         = stream(id);
    this.pluginId   = stream(pluginId);
    this.properties = stream(properties);

    ValidatableMixin.call(this);
    this.validatePresenceOf("pluginId");
    this.validatePresenceOf("id");
    this.validateFormatOf("id",
                          new RegExp("^[-a-zA-Z0-9_][-a-zA-Z0-9_.]*$"),
                          {message: "Invalid Id. This must be alphanumeric and can contain underscores and periods (however, it cannot start with a period)."});
    this.validateMaxLength("id", 255, {message: "The maximum allowed length is 255 characters."});
  }