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Aggregation and Functional dependency in DBMS-computer world


 Aggregation and Functional dependency in DBMS


Aggregation 

In aggregation the relation between two entities is treated as a single entity. In aggregation relationship with its corresponding entity is aggregated into higher level entity . It is the process of compiling information on object, there by obstructing a higher level. On limitation of the ER model is that it can not Express relationship among relationships. The aggregation represent a relationship between a whole object and its component in other word we can say that using aggregation we can express relationship main relationships.

 For example center entity offer the course entity act as a single entity in the relationship which is in a relationship with another entity visitor. In the real world if a visitor visits a coaching center they will never inquiry about the course or just about the center instead he will ask the inquiry about both.

Functional dependency

 Functional dependency play an important role in differentiating good database resign from not so good database region functional dependency are conservation of the internal relationship among attribute of an entity represent by relation functional dependency is a relationship the exist attribute it typically exist between the primary key and non key attribute within a table in other words we can say that functional dependency in DBMS, as the name suggest in a relationship between attribute of a table dependent on each other it helps in preventing data and gets to know about bad design.


In this example if we know the value of employee number , we can obtain employee name, City , salary etc. By this we can say that the employee city, employee name and employee salary are functionally dependent on employee number.

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