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Relational Data Model in Database

Relational Data Model in Database

  1. Each column in a row must be single valued.
  2. Primary key field value cannot be null.
  3. Primary key must contain unique value.
  4. Foreign key can be null.
  5. Foreign key constraint can contain null values(blank).
  6. If Foreign key is not null , then it must have values that correspond to the value of a primary key in an other relation.
  7. 3NF is adequate for relational database design.
  8. In BCNF we may loose some functional dependencies.

All meta data is stored in Data Dictionary in Databse

   All meta data is stored in Data Dictionary in Databse

Database schema (definition of table structure) including field name and it's data type ,other constraints like primary key , integrity constraints etc are stored in data dictionary.

Structural dependence vs Structural independence in Database

 

Structural dependence  vs Structural independence  in Database

Structural Independence

Structural independence exist when changes in the database structure do not affect DBMS ability to access data.

Structural Dependence 

 Structural dependence exist when changes in the database structure affect DBMS ability to access data.

File System exhibit Structural Dependence   

A file system exhibit structural dependence because a change in any file structure such as(addition or deletion of a field) require modifications of all programs using that file.

File System exhibit Data Dependence

A file system is said to exhibit data dependence because a change in any file's data characteristic such as changing the field from integer to decimal requires changes in all data access programs. That means access to a file data is dependent on it's data characteristics.

 

Hierarchical Database Model does not support Structural Independence.

Hierarchical Database Model does not support structural independence.