Database-MySQL [3i Infotech Placement]: Sample Questions 145 - 146 of 162

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Question 145

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Describe in Detail

Essay▾

Explain Normalization and Denormalization with examples.

Explanation

Normalization

  • It is the process of organizing data into related table.
  • To normalize database, we divide database into tables and establish relationships between the tables.
  • It reduces redundancy. It is done to improve performance of query.

    Steps of normalization:

  • First Normal form
    • Entities of the table must have unique identifier or entity key.
    • Second Normal Form
    • All the attributes of the table must depend on the entity key for that entity.
    • Third Normal Form
    • All attributes that are not part of the key must not depend on any other non-key attributes.

    Example of Normalization:

Normalization Process

De-normalization

  • The process of adding redundant data to get rid of complex join, in order to optimize database performance.
  • This is done to speed up database access by moving from higher to lower form of normalization.

Example of De-normalization

Example of De-Normalization

Question 146

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Describe in Detail

Essay▾

What is Data Independence?

Explanation

  • Data independence is ability to modify a schema definition in one level without affecting a schema definition in the next higher level.
  • There are two levels of data independence:
    • Physical Data Independence
    • Logical Data Independence

    These are described below:

  • Physical Data Independence:
    • Physical Data Independence is the ability to modify the physical schema without requiring any change in application programs.
    • Modifications at the internal levels are occasionally necessary to improve performance. possible modifications at internal levels are change in file structures, compression techniques, hashing algorithms, storage devices, etc.
    • Physical data independence separates conceptual levels from the internal levels.
    • This allows to provide a logical description of the database without the need to specify physical structures.
    • Comparatively, it is easy to achieve physical data independence.
  • Logical Data Independence:
    • Logical data independence is ability to modify the conceptual schema without requiring any change in application programs.
    • Modification at the logical levels are necessary whenever the logical structures of the database is altered.
    • Logical data independence separates external level from the conceptual view.
    • Comparatively it is difficult to achieve logical data independence.
    • Application programs are heavily dependent on logical structures of the data they access. so any change in logical structure also requires programs to change.

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