Database-MySQL [3i Infotech Placement]: Sample Questions 50 - 50 of 162

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Question 50

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Describe in Detail

Essay▾

Describe the three levels of data abstraction?

Explanation

The Three Levels of Data Abstraction

Physical Level:

  • It is the lowest level of abstraction and describes how the data in the database are actually stored.
  • This level describes complex low-level data structures in detail and is concerned with the way the data is physically stored.
  • Data only exists at physical level.

Logical Level:

  • This is the next higher level of abstraction and describes what data are stored in the database, and what relationships exist among those data.
  • It describes the structure of whole database and hides details of physical storage structure.
  • It concentrates on describing entities, data types, relationships, attributes and constraints.
  • All of the views must be derivable from this conceptual schema.

View Level:

  • It is the highest level of abstraction and is concerned with the way the data is seen by individual users.
  • This level simplifies the users՚ interaction with the system.
  • It includes a number of user views and hence is guided by the end user requirement.
  • It describes only those part of the database in which the users are interested and hides rest of all from those users.
  • Each user group refers to its own external schema.

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