 Models are idealized systems known to be incorrect but assumed to be close enough to provide reliable predictors for the predefined areas of interest within a domain.A description, on the other hand, is a recording of facts or beliefs about something within the realm of an individual’s knowledge or experience.Such descriptions are generally incomplete; that is, the person giving a description may omit facts that he or she believes are irrelevant, or which were forgotten in the course of describing the system.