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Short notes on database schema & database independence- computer science fundamentals tutorial


            Database Schema & Data Independence

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       Database Schema: - A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how relation among them are associated.  Database schema  formulates all the constrains that are to be applied on the data.
A database schema defines its entities and the relationship among them. It contains descriptive details of the database which can be described by means of schema diagram. A database schema can be divided into two categories.

  I.  Physical database schema: - this schema contain to the actual storage of data and its form of storage like files, indices etc. It defines how the data will be stored in a secondary storage.
 II. Logical database schema: - this schema defines all the logical constrains that need to be applied on the data stored. It defines tables, views and integrality constrains.


    Data Independence: - Data Independence can be explained using    3three schema architecture. Data independence refers characteristic of being able to modified schema at one level of the database without altering the schema at next higher level.
      There are two types of data independence.
    I. Logical data independence: - It refers characteristic being able to change conceptual schema without having to change the external schema. Logical data independence is used to separate the external level from conceptual view. Logical data independence occurs at user inference level.


    II. Physical data independence:- Physical data independence can be defined as capacity to change internal schema without having to change conceptual schema. Physical data independence used to separate conceptual level from internal level. Physical data independence occurs at the logical interference level. 
Data independence
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