Object-Oriented terminology

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Introduction

 * What is a class?
 * Functions of classes

Modelling and validating a model

 * Level 0 in the university example are the objects so In the example below the objects or instances are of level 0.
 * The classes are level 1 (diagram or model level).
 * Modelling: Modelling is abstracting, it means that you make the transition from level 0 to level 1. You go from the instances to the definition of the concepts.
 * Validating a model: On the other hand when you want to validate the model you have to do the reverse. So you will take the model and reason on an example. You will start from level 1 and you will try to illustrate this level 1 by finding a level 0 example that proves or disproves that your model is right.

Tangible and intangible objects
Notice that classes can represent both tangible and intangible objects. Students are for example tangible objects while study programs are intangible objects. Both kinds of objects can be represented as classes in the UML class diagram.