aggregateValidationStatus.addChangeListener(new IChangeListener() {
			public void handleChange(ChangeEvent event) {
				System.out.println("changed");
				boolean formIsValid = true;
				aggregateValidationStatus.getValue();
				for (Object o : dataBindingContext.getBindings()) {
					Binding binding = (Binding) o;
					IStatus status = (IStatus) binding.getValidationStatus().getValue();
					if (!status.isOK()) {
						formIsValid = false;
					}

					Control control = null;
					if (binding.getTarget() instanceof ISWTObservable) {
						ISWTObservable swtObservable = (ISWTObservable) binding.getTarget();
						control = (Control) swtObservable.getWidget();
					}
					if (binding.getTarget() instanceof CalendarComboObservableValue) {
						CalendarComboObservableValue observable = (CalendarComboObservableValue) binding.getTarget();
						control = (Control) observable.getControl();
					}

					if (binding.getTarget() instanceof IViewerObservable) {
						IViewerObservable observable = (IViewerObservable) binding.getTarget();
						control = observable.getViewer().getControl();
					}

					ControlDecoration decoration = decoratorMap.get(control);
					if (decoration != null) {
						if (status.isOK() || status.matches(Status.WARNING)) {
							decoration.hide();
						} else {
							decoration.setDescriptionText(status.getMessage());
							decoration.show();
						}
					}
				}
				if (saveBtn != null)
					saveBtn.setEnabled(formIsValid);
			}
		});

	private class PeriodValidator extends MultiValidator {

		private IObservableValue start;
		private IObservableValue end;

		public PeriodValidator(IObservableValue start, IObservableValue end) {
			System.out.println("create validator");
			this.start = start;
			this.end = end;
		}

		@Override
		protected IStatus validate() {
			Date startDate = (Date) start.getValue();
			Date endDate = (Date) end.getValue();

			if (start != null && end != null) {
				if (startDate.after(endDate)) {
					return ValidationStatus.error("From is after To");
				}
			}
			return ValidationStatus.OK_STATUS;
		}
	}

		dbFactory.addBinding(periodFromCalendar, "timePeriodFrom",
				new UpdateValueStrategy(UpdateValueStrategy.POLICY_UPDATE)
						.setConverter(new Converter(Date.class, Date.class) {

							@Override
							public Object convert(Object fromObject) {
								Calendar c = Calendar.getInstance();
								c.setTime((Date) fromObject);
								c.set(Calendar.DAY_OF_MONTH, 1);
								return c.getTime();
							}
						}),
				new UpdateValueStrategy(UpdateValueStrategy.POLICY_UPDATE));

		dbFactory.addBinding(periodToCalendar, "timePeriodTo",
				new UpdateValueStrategy(UpdateValueStrategy.POLICY_UPDATE)
						.setConverter(new Converter(Date.class, Date.class) {

							@Override
							public Object convert(Object fromObject) {
								Calendar c = Calendar.getInstance();
								c.setTime((Date) fromObject);
								c.set(Calendar.DAY_OF_MONTH, c.getActualMaximum(Calendar.DAY_OF_MONTH));
								return c.getTime();
							}
						}),
				new UpdateValueStrategy(UpdateValueStrategy.POLICY_UPDATE));

		dbFactory.addValidationStatusProvider(
				new PeriodValidator(new CalendarComboObservableValue(periodFromCalendar, SWT.Modify),
						new CalendarComboObservableValue(periodToCalendar, SWT.Modify)));