" MVC is often thought of as a software design pattern. However, MVC encompasses more of the architecture of an application than is typical for a design pattern . Hence the term architectural pattern may be useful (Buschmann, et al 1996), or perhaps an aggregate design pattern. Operation In broad terms, constructing an application using an MVC architecture involves defining three classes of modules. Model: This is the domain-specific representation of the information on which the application operates. The model is another name for the domain layer. Domain logic adds meaning to raw data e. Model Train Shopg. calculating if today is the user's birthday or the totals, taxes and shipping charges for shopping cart items. "

" That justifies talking about their purpose prior to talking about their consistency. Models are used as substitutes for originals because properties of the latter are of interest and the originals are not going to be investigated themselves. There may be a number of reasons for that such as taboos preventing from studying the original itself, or inability, the involved cost in terms of resources or moral damage being intolerable, or similar. For an investigator I it makes only sense to consider an entity M as a substitute of an entity O, if I can (1) establish an analogy, similarity, or similar relation between M and O that permits the substitution of O by M with respect to purpose and means, time-horizon etc. , and (2) I can actually investigate M in the required way. That implies firstly that M does not have the properties of O that prevent I from investigating O. Also other properties of O may not be properties of M. Model Train Track In that sense a model is more abstract than its original. Secondly, a model M will in general have properties that O does not have and that actually aid I in investigating M. "