DBMS Notes

Schema in DB

  • The Schema is the logical structure of any relation (table).
  • The collection of schemas of all tables’ for an entire database is know as database schema.
  • To implement Schema, data definition languages (DDL) of SQL are used. DDL involves i.e. create table, delete table, update table etc.

Keep In mind

Data is present in the form of file in Database storage. Data does not exist in the form of table in database storage.

Data is retrieved in the form of table from database and then various operations performed on it.  

Below diagram represents the Schema of different tables (student, course, section, Grade) of entire database.

Term Instance

If in a table (student), there are 5 entries then each entry is the instance of table (Student). So total 5 instances of this table
so we can say

  • The data store in the database at a particular moment of time, is an instance of that database.

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