"F. Novaes, Standard Model: An Introduction, hep-ph:0001283 I . Models are usually man-constituted. 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. Virtual Girl Model, 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. "

" The model is another name for the domain layer. Domain logic adds meaning to raw data e. g. calculating if today is the user's birthday or the totals, taxes and shipping charges for shopping cart items. View: This renders the model into a form suitable for interaction, typically a user interface element. MVC is often seen in web apps: the view is the html page and the code which gathers dynamic data for the page. Controller: This responds to events, typically user actions, and invokes changes on the model (but *not* the view). Virtual Wedding Dress Model Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention this data access layer. "