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You face a classic problem that arises whenever users and technicians need to speak about a
Users think in a logical way. They divide the database in entities and concepts that are
directly related to their view of the topic, which is much related to the real world. In this
example, they see products as entities, and categories and subcategories as simple
textual descriptions attached to the products. In the user’s world, there is no need to think
about a table containing all the categories, nor do they understand why any
relationships should exist among those tables.
Technicians, on the other hand, think in a physical way. They divide the database in
technical entities that are very much related to the physical representation of data on a disk.
In the technical world, it is obvious that if products have categories and subcategories, the
most effective way to store this information is through three different tables and a set of
relationships among them. The physical representation on a disk aims at the reduction of
data duplication, to avoid inconsistencies. This technique is known as data normalization .
Data normalization is the reason for having so many tables in a relational database. You
learn more about normalization in the next paragraphs.
So there are always at least two distinct ways to look at a database. We refer to the two views
as the logical (user) versus physical (technician) one. Users think logically; technicians think
physically. We can look at Figure 4-15 to better appreciate the difference between the two
representations of the same item: a product. On the left side of the figure, you see three tables
and two relationships—the technical view. On the right side, you see the simpler user view of a
product, which is composed of a single entity.
FIguRE 4-15 Different ways to see products: from the technician (on the left) and the user (right) points of view.
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