Importance of Join Dependencies
Join dependency can be very important for several reasons as it helps in maintaining data integrity, possess normalization, helps in query optimization within a database. Let us see each point in a detail:
- Data Integrity: Join Dependency helps maintain data integrity in a database. Database designers can make sure that the queries are consistent after checking for the dependencies. Like in lossless join dependency no information is lost, which means data is accurate. This will remove the data that is not accurate. Similarly, a join dependency is a constraint that maintains data integrity.
- Query Optimization: Query optimization leads to improving the performance of the database system. The database designers can choose the best join order to execute the queries which in turn reduces the computational costs, memory utilization and i/o operations to get the queries executed quickly.
Join Dependencies in DBMS
Join Dependency (JD) can be illustrated as when the relation R is equal to the join of the sub-relations R1, R2,…, and Rn are present in the database. Join Dependency arises when the attributes in one relation are dependent on attributes in another relation, which means certain rows will exist in the table if there is the same row in another table. Multiple tables are joined to create a single table where one of the attributes is common in the sub-tables. We can also relate the join dependency to the 5th Normal Form. A join dependency is said to be not that important if any relational schemas in the join dependency are equivalent to the original relation R.
Join dependency on a database is denoted by:
R1 ⨝ R2 ⨝ R3 ⨝ ….. ⨝ Rn ;
where R1 , R2, … , Rn are the relations and ⨝ represents the natural join operator.