Friday, 23 October 2020

Attribute Inheritance in DBMS

 

Attribute Inheritance:

 

The attribute inheritance is an important property of higher and lower level entities created by specialization and generalization. The attributes of the higher-level entity sets are said to be inherited by the lower-level entity sets. For ex: customer and employee inherit the attributes of person. Thus, customer is described by its name, street, and city attributes, and additionally a customer-id attribute. While employee is described by its name, street, and city attributes, and additionally employee-id and salary attributes.

 

A lower-level entity set (or subclass) also inherits participation in the relationship sets in which its higher-level entity (or superclass) participates. Attribute inheritance applies through all tiers of lower-level entity sets.

 

Attribute Inheritance - Specialization and Generalization
Fig: Specialization and Generalization

The above fig. (Fig: Specialization and Generalization) depicts a hierarchy of entity sets. In the fig., employee is a lower-level entity set of person and a higher-level entity set of the officer, teller, and secretary entity sets. The entity sets in this diagram have only single inheritance. If an entity set is a lower-level entity set in more than one ISA relationship, then the entity set has multiple inheritance, and the resulting structure is said to be a lattice.

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