The Model is the guts of your application: what it actually does. It might be, for instance, the database of tunes on your device and the code for playing them. It might be your list of contacts and the code that places phone calls or sends IMs to them.
While a particular application's View and Controller will necessarily reflect the Model they manipulate, a single Model might be used by several different applications. Think, for instance, of an MP3 player and an application that converts MP3 files into WAV files. For both applications, the Model includes the MP3 file format and codecs for it. The former application, however, has the familiar Stop, Start, and Pause controls, and plays the track. The latter may not produce any sound at all; instead, it will have controls for setting bitrate, etc. The Model is all about the data. It is the subject of most of the rest of this book.
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