Specialization and Aggregation.
1 Answer

Specialization is opposite to Generalization. It is a top-down approach in which one higher level entity can be broken down into two lower level entity. In specialization, some higher level entities may not have lower-level entity sets at all.

Take a group ‘Person’ for example. A person has name, date of birth, gender, etc. These properties are common in all persons, human beings. But in a company, persons can be identified as employee, employer, customer, or vendor, based on what role they play in the company.

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Similarly, in a school database, persons can be specialized as teacher, student, or a staff, based on what role they play in school as entities.


Aggregation is the process of compiling information on an object, thereby abstracting a higher level object. So, an entity Person is derived by aggregating the characteristics name, house_no., city and social security number (SSN).

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Another form of aggregation says that it is abstracting a relationship between objects and viewing the relationship as an object. So, in Figure 3, the Enrollment relationship between entities student and Course entity can be viewed as entity REGISTRATION.

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In simple terms, Aggregation is a process when relation between two entities is treated as a single entity.

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