Descriptions and Models
The distinction between descriptions and models, though subtle, is an important one in IDEF3, and both have a precise technical meaning.
- The term description is used as a reserved technical term to mean records of empirical observations; that is, descriptions record knowledge that originates in or is based on observations or experience.
- The term model is used to mean an idealization of an entity or state of affairs. That is, a model constitutes an idealized system of objects, properties, and relations that is designed to imitate, in certain relevant respects, the character of a given real-world system. Frictionless planes, perfectly rigid bodies, the assumption of point mass, and so forth are representative examples of models.
The power of a model comes from its ability to simplify the real-world system it represents and to predict certain facts about that system by virtue of corresponding facts within the model. Thus, a model is a designed system in its own right. 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. Descriptions may also be inconsistent with respect to how others have observed situations within the domain. IDEF3 accommodates these possibilities by providing specific features enabling the capture and organization of alternative descriptions of the same scenario or process, see figure.
Read more about this topic: IDEF3, IDEF3 Basic Concepts
Famous quotes containing the words descriptions and/or models:
“Our Lamaze instructor . . . assured our class . . . that our cervix muscles would become “naturally numb” as they swelled and stretched, and deep breathing would turn the final explosions of pain into “manageable discomfort.” This descriptions turned out to be as accurate as, say a steward advising passengers aboard the Titanic to prepare for a brisk but bracing swim.”
—Mary Kay Blakely (20th century)
“Grandparents can be role models about areas that may not be significant to young children directly but that can teach them about patience and courage when we are ill, or handicapped by problems of aging. Our attitudes toward retirement, marriage, recreation, even our feelings about death and dying may make much more of an impression than we realize.”
—Eda Le Shan (20th century)