Database Chapter Concepts | Class 11 Informatics Practices Notes

a) Relation or Table b) Data Dictionary or Metadata c) Primary Key d) NULL value e) Candidate Key or Alternate Key f) Database Management System (DBMS)

Foreign keys are allowed to have NULL values because a foreign key represents a reference to a primary key in another table, and sometimes the relationship may be optional. When there is no related tuple in the referenced table, the foreign key can be NULL to indicate the absence of a relationship.

Example: Consider two tables, STUDENT and SPORTS_PREFERENCE. If a student has not chosen any sport, the foreign key in SPORTS_PREFERENCE referring to STUDENT's primary key can be NULL, indicating no

a) Database Schema vs Database State:

• Schema is the structure or design of the database, defined by tables, attributes, and constraints. It is fixed and does not change frequently.
• State is the actual data stored in the database at a particular moment. It changes as data is inserted, updated, or deleted.

b) Primary Key vs Foreign Key:

• Primary key uniquely identifies each tuple in a relation.
• Foreign key is an attribute in one relation that refers to the primary key in another relation t

A DBMS avoids redundancy by storing data in a structured way using relations (tables) and enforcing constraints such as primary keys and foreign keys. It normalizes data to eliminate duplicate storage and maintains data consistency by centralizing data management. Unlike file systems where data is stored in separate files leading to duplication, DBMS uses relationships and keys to store data only once and reference it as needed.