What are different types of Database users and their roles? Explain the Data independence with example.

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The users of the database can be classified into the following groups −

  1. Native users − The native users need not be aware of the presence of the database system. They are end-users of the database who works through menu-driven application programs, where the type and range of response are always indicated to the user
  2. Online users − Online users may communicate with databases directly through an online terminal or indirectly through user interfaces and application programs.
  3. Sophisticated Users − They are those users who interact with the system without writing the program instead they form their requests in the database query language. They are the SQL programmers, who are going to deal directly with the database. They write queries to delete or select or insert and update the database.
  4. Specialized Users − Specialized users who write specialized database applications that do not fit into the fractional database processing framework.
  5. Application Programmer − The application programmer users who are responsible for developing the application programs or user interface. The application programs could be written in a high-level language. For example − Java, .net, PHP etc,
  6. Database Administrator (DBA) − It is a person or the group in charge of implementing the database system within the organization. The DBA has all the privileges allowed by the DBMS and can assign or remove the privileges from the users.

Data independence is the ability to modify the scheme without affecting the programs and the application to be rewritten. Data is separated from the programs so that the changes made to the data will not affect the program execution and the application.

There are two levels of data independence based on three levels of abstraction. These are as follows −

  • Physical Data Independence
  • Logical Data Independence

Logical Data Independence:

The capacity to change the conceptual schema without having to change the external schemas and their associated application programs is called logical data independence. When the modification is done to the conceptual schema (i.e tables) the mapping called “external mapping” is changed automatically by DBMS.

Examples of changes under Physical Data Independence

Due to Physical independence, any of the below changes will not affect the conceptual layer.

  • Using a new storage device like Hard Drive or Magnetic Tapes
  • Modifying the file organization technique in the Database
  • Switching to different data structures.
  • Changing the access method.
  • Modifying indexes.
  • Changes to compression techniques or hashing algorithms.
  • Change of Location of Database from say C drive to D Drive

Physical Data Independence:

The capacity to change the internal schema without having to change the conceptual schema is called physical data independence. When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS. This mapping is called “logical mapping”.

For example, the internal schema may be changed when certain file structures are reorganized or new indexes are created to improve database performance.

Examples of changes under Logical Data Independence

Due to Logical independence, any of the below changes will not affect the external layer.

  1. Add/Modify/Delete a new attribute, entity or relationship is possible without a rewrite of existing application programs
  2. Merging two records into one
  3. Breaking an existing record into two or more records
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