WHAT IS GENERALIZATION ? DISCUSS ABOUT GENERALIZATION
GENERALIZATIONà Consider the entity set ACCOUNT with Attributes à Acc-No & BALANCE Each Account Contains
1. SAVINGS-ACCOUNT
2. CHECKING-ACCOUNT
Each of these is described by a set of attributes which includes all the attributes of entity set. ACCOUNT PLUS additional attributes . For example SAVINGS-ACCOUNT entities are described further by the attributes INTEREST-RATE while CHECKING ACCOUNT are described further by the attributes OVERDRAFT – AMOUNT. These are similarities between the CHECKING-ACCOUNT entity set and the SAVINGS ACCOUNT entity set in the sense that they have several attributes in common. This commonality can be expressed by generalization which is a containment relationship that exist between a higher level ENTITY set and one or more lower level entity sets . In the above example, ACCOUNT is the higher level entity set and SAVINGS-ACCOUNT and CHECK a ACCOUNT are lower level entity set.
In term of an E-R diagram, generalization is depleted through a triangle component labled is a as shown in following figure. The table ‘ISA’ stands for “is a” and represent that a SAVINGS-ACCOUNT “is an” ACCOUNT.
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