Models and representations

Abstract

A model is a representation of something; it is an abstraction. The thing being modeled need not be real — think of plastic models of the starship Enterprise. In this case the thing is imaginary while the model is real. Models are typically built to aid understanding. Also, because they are abstractions that omit inessential details, they are often easier to construct and manipulate than the thing they represent. However, as we shall see, an information model is not necessarily simple, either to create or to manipulate. We distinguish two sorts of model here, namely a conceptual model and a concrete model. Definition 4 A conceptual information model is independent of any particular instantiation form. Definition 5 A concrete model is an information model that is specialized to take account of a particular instantiation method. (This is what is typically known as a data model.) An information (data) model may be instantiated or populated to represent collections of particular ideas, facts or processes. Definition 6 An instantiated model consists of the data that represents instances of the things defined in an information model. We are principally concerned with conceptual information models. A conceptual model is a view about real world information and is itself, therefore, communicable information. The model needs to be organized in such a manner to aid understanding by the recipient, which will essentially be a human as opposed to a computer system; even if the intended recipient is a software system this is still a human artifact. Before examining ways of representing models it is useful to look briefly at some of the methods that we humans use to organize our thoughts. There are some organizing principles and concepts that we seem to use time after time, whether consciously or unconsciously. We tend to group things into categories or classes. Each member of a category has some aspects that are common to other members and some individual aspects. For example, we can talk about vehicles in general with one common aspect being that a vehicle provides a means of transportation. Within the general vehicle class we might split it up into sub-categories of truck, bus and car.