For example, a university application has a "student" application object. The user sees a visual representation of a student, which might be a textual representation, a graphical representation (such as a form with name, address, and student id number), or even an image of the face of the student. The presentation type of the student is "student"; that is, the semantic type of the object that appears on the screen is "student." Since the type of a displayed object is known, CLIM knows which operations are appropriate to perform on the displayed object. For example, when a student is displayed, it is possible to perform operations such as send-tuition-bill or show-transcript .
Common Lisp Interface Manager 2.0 User's Guide - 20 Sep 2011