The main purpose of the system is its usability and therefore the retrieval of data from the database should be made very efficient. Since many database system users are not computer trained, developers hide the complexity from users through several levels of abstraction, to simplify the user’s interaction with the system. The three main levels of abstraction are:
Physical Level: The lowest level of abstraction describes how the data is actually stored. The physical level describes complex low-level data structures in detail.
Logical Level: A higher level of abstraction describes the data stored in the database and the relationships that exists among the data. It describes the entire database in a relatively simple data structure.
View Level: The highest level of abstraction describes only part of the entire database. Even though the logical level uses a simpler structure, complexity remains because of the variety of information stored in a large database.
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