Data Views:
A DBMS allows users to access and modify the files, even without actually knowing where and how the data physically exists. There are various types of views that allow the users to access the required data in the database system. These views are described in the form of data abstraction, instances, and schemas.
Data abstraction
The main objective of a DBMS is to provide the users with an abstract view of the database system. The system hides certain details from the users as to how the data is created, stored, and maintained. In other words, the users are not provided with intricate information about the database system. The system manages to hide certain details by defining three levels of abstraction - the physical level, the logical level, and the view level. Denotes the figure for the various levels of abstraction. The need for storing and retrieving data efficiently has led to the design of complex data structures for the representation of data in the database.
Physical level: The lowest level of abstraction describes the manner in which data is actually stored. At the physical level, complex low-level data structures are described in detail. An example of physical level abstraction is machine level programming.
Logical level: The logical level is the next level of abstraction that describes the type of data stored in the database, and their interrelationships. This is also known as the conceptual level. The entire database is described in terms of a small number of relatively simple structures. At the logical level, each record is described by a type definition. The interrelationship among these record types is also defined. Programmers and DBAs usually work at this level of abstraction. An example of logical level abstraction is programming logic.
View level: The view level is the highest level of abstraction. Despite the use of simpler structures at the logical level, some complexity remains, because of the large size of the database. Interaction with the system is simplified by the DBMS software and users need to access only a part of the database. The system provides many views for the same database.
The database system hides many of the lowest-level storage details from database programmers. Only DBAs may be aware of the physical organization of the data. At the view level, the users see a set of application programs that hide the details of the data types. In addition to hiding details of the logical level, the views also provide a security mechanism to prevent users from accessing parts of the database. An example of view level abstraction is an application being used by end users.
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