Validation Rule To Validate Against Different Model Attribute

Hi,


I have a model 'Isshortlisted' which have attributes appoint_date and appoint_time. Also i have a model 'Job' which have attributes start_appoint_date, end_appoint_date, start_appoint_time, end_appoint_time. I want someone like admin to set the attributes of 'Isshortlisted' (appoint_date, appoint_time) in between the values given in the attributes of job model. I have been searching for custom validation functions to define a validation rule in the 'Isshortlisted' model so that admin can't give a wrong value but have found nothing useful. Please help me in this regard...