21.-2.4 - As we discussed in the previous section there are...

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As we discussed in the previous section there are many types of persons involved in the development, management and use of a database: database designers, programmers, end users. Each of these types see the data in a different way, characteristic to their need of using or processing the data. In order to assist the communication between these persons and reconcile their different view, various data models are created. Moreover, having models at different degrees of abstractions allow varying views of the same data. 1
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2 In general, a model is an abstraction of a real-world object or event. It is useful in understanding the complexities of the real-world environment. To create a representation of the data structures from the real-world, we are using data models, which offer a simplified view, often using a graphical form. The data modeling process is an iterative process, when based on the requirements more and more complex models are created.
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3 We will discuss about some basic building blocks for the data modeling. An ENTITY is anything about which data are to be collected, stored and process. Let us take some examples. In the following phrases try to identify the entities.
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21.-2.4 - As we discussed in the previous section there are...

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