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.
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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