/// <summary>
        /// (1) checks if remaining vacation days of employee suffice, 
        /// (2) sets lock period flag if appropriate,
        /// (3) sets vacation period overlap flag if appropriate
        /// </summary>
        /// <param name="VacationRequest"> a vacation request, passed by reference</param>
        /// <returns></returns>
        public Boolean Validate(VacationRequest VacationRequest)
        {
            Boolean result = false;

            ///<remarks> this value must be numeric</remarks>
            //checks remaining vacation days
            DBQuery dbq = new DBQuery();
            int remainingVacationDays = dbq.SelectRemainingVacationDays(VacationRequest.getEmployeeID());

            // determine working days in vacation request
            int vacationWorkingDays = VacationRequest.DetermineWorkingDaysInVacationRequest(VacationRequest);

            // only proceed if time period of vacation request contains working days
            if (vacationWorkingDays > 0)
            {
                VacationRequest.setNetVacationDays(vacationWorkingDays);

                // Check  VacationRequest overlap with others already existing VacationRequests of Requester without state "canceled"
                var VRList = dbq.SelectUncanceledEmployeeVacationRequestInTimePeriod(VacationRequest, VacationRequest.getEmployeeID());

                Boolean overlap = false;
                Boolean insufficientRemainingVacationDays = false;

                if (VRList.Count > 0)
                {
                    overlap = true;
                    ErrorState.ErrorStateInstance.setError(ErrorState.OVERLAP_WITH_OWN_VACATION_REQUEST);
                }
                if (remainingVacationDays < vacationWorkingDays)
                {
                    insufficientRemainingVacationDays = true;
                    ErrorState.ErrorStateInstance.setError(ErrorState.INSUFFICIENT_REMAINING_VACATION_DAYS);
                }
                // if requester has enough remaining Vacation Days AND no submitted vacation request(s) in this time period, go ahead
                if (!insufficientRemainingVacationDays && !overlap)
                {
                    TimePeriodOverlapCheck check = new TimePeriodOverlapCheck(VacationRequest);

                    //check lock period
                    if (!check.Validate(TimePeriodOverlapCheck.CHECK_CATEGORY_LOCK_PERIOD))
                    {
                        //overlap existing
                        VacationRequest.setVacationLockPeriodNote(true);
                    }

                    //check overlap period with Deputy
                    if (!check.Validate(TimePeriodOverlapCheck.CHECK_CATEGORY_VACATION_OVERLAP_PERIOD))
                    {
                        //overlap existing
                        VacationRequest.setVacationPeriodOverlapNote(true);
                    }

                    if (VacationRequest.getVacationStartDate() < DateTime.Now)
                    {
                        //if VacationRequestEndDate is in past the new Processingstatus is: agreed, so the decision of the DivisionManager is the next step
                        VacationRequest.setVacationRequestProcessingState(VacationRequestProcessingState.agreed);
                    }
                    result = true;
                }
            }
            else
            {
                ErrorState.ErrorStateInstance.setError(ErrorState.ZERO_NET_VACATION_DAYS_IN_VACATION_REQUEST);
            }
            return result;
        }