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Q1. Define Data Model & discuss the categories of Data Models? What is the difference between logical data Independence & Physical Data Independence?


Answer:
Data Model :
  • It is a set of Concepts for viewing a set of data in a structured way.
  • This can be easily understood by professionals and nontechnical users.
  • It can explain the way in which the organization uses and manages the information.

categories  of Data Model:
Entity
  • An entity is something that has a distinct, separate existence, though it need not be of a material existence.
E.g. - Employee.
Attribute
  • It is the property that describes an entity
  • It is a characteristic or property of an object, such as weight, size, or color
Relationship
  • Describes the relationship between two or more entities

Logical data independence:
This is the ability to modify the conceptual scheme without causing application programs to be rewritten. This is usually done when the logical structure of database is altered. Logical data independence is harder to achieve, as the application programs are usually heavily dependent on the logical structure of the data. An analogy is made to abstract data types in programming languages.

Physical data independence:
This is the ability to modify the physical scheme without causing application programs to be rewritten. Modifications at this level are usually to improve performance.

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