Generalization
o Generalization is like a bottom-up approach in which two or more entities of
lower level combine to form a higher level entity if they have some attributes
in common.
o In generalization, an entity of a higher level can also combine with the entities
of the lower level to form a further higher level entity.
o Generalization is more like subclass and superclass system, but the only
difference is the approach. Generalization uses the bottom-up approach.
o In generalization, entities are combined to form a more generalized entity, i.e.,
subclasses are combined to make a superclass.
For example, Faculty and Student entities can be generalized and create a higher
level entity Person.
Aggregation
In aggregation, the relation between two entities is treated as a single entity. In
aggregation, relationship with its corresponding entities is aggregated into a higher
level entity.
,For example: Center entity offers 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 then he will never enquiry about the Course only or
just about the Center instead he will ask the enquiry about both.
Reduction of ER diagram to Table
The database can be represented using the notations, and these notations can be reduced to a
collection of tables.
In the database, every entity set or relationship set can be represented in tabular form.
The ER diagram is given below:
, There are some points for converting the ER diagram to the table:
o Entity type becomes a table.
In the given ER diagram, LECTURE, STUDENT, SUBJECT and COURSE forms individual
tables.
o All single-valued attribute becomes a column for the table.
In the STUDENT entity, STUDENT_NAME and STUDENT_ID form the column of
STUDENT table. Similarly, COURSE_NAME and COURSE_ID form the column of
COURSE table and so on.
o A key attribute of the entity type represented by the primary key.
In the given ER diagram, COURSE_ID, STUDENT_ID, SUBJECT_ID, and LECTURE_ID are
the key attribute of the entity.
o The multivalued attribute is represented by a separate table.
In the student table, a hobby is a multivalued attribute. So it is not possible to
represent multiple values in a single column of STUDENT table. Hence we create a
o Generalization is like a bottom-up approach in which two or more entities of
lower level combine to form a higher level entity if they have some attributes
in common.
o In generalization, an entity of a higher level can also combine with the entities
of the lower level to form a further higher level entity.
o Generalization is more like subclass and superclass system, but the only
difference is the approach. Generalization uses the bottom-up approach.
o In generalization, entities are combined to form a more generalized entity, i.e.,
subclasses are combined to make a superclass.
For example, Faculty and Student entities can be generalized and create a higher
level entity Person.
Aggregation
In aggregation, the relation between two entities is treated as a single entity. In
aggregation, relationship with its corresponding entities is aggregated into a higher
level entity.
,For example: Center entity offers 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 then he will never enquiry about the Course only or
just about the Center instead he will ask the enquiry about both.
Reduction of ER diagram to Table
The database can be represented using the notations, and these notations can be reduced to a
collection of tables.
In the database, every entity set or relationship set can be represented in tabular form.
The ER diagram is given below:
, There are some points for converting the ER diagram to the table:
o Entity type becomes a table.
In the given ER diagram, LECTURE, STUDENT, SUBJECT and COURSE forms individual
tables.
o All single-valued attribute becomes a column for the table.
In the STUDENT entity, STUDENT_NAME and STUDENT_ID form the column of
STUDENT table. Similarly, COURSE_NAME and COURSE_ID form the column of
COURSE table and so on.
o A key attribute of the entity type represented by the primary key.
In the given ER diagram, COURSE_ID, STUDENT_ID, SUBJECT_ID, and LECTURE_ID are
the key attribute of the entity.
o The multivalued attribute is represented by a separate table.
In the student table, a hobby is a multivalued attribute. So it is not possible to
represent multiple values in a single column of STUDENT table. Hence we create a
