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Which of the following features is supported in the rational database model?

  1. Complex data-types
  2. Multivalued attributes
  3. Associations with multiplicities
  4. Generalization relationships
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answer D

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Composite attributes or Multi-valued attributes are not allowed. Composite attributes are generally sub-divided while for multi-valued attributes a new relation is created.

Complex data type: It is composite of other traditional data types such as character, numeric, date etc. Examples include maps, images, videos, time-series etc. They are generally stored as objects. Complex dataypes are generally not allowed in relational database.

Association is the relationship between two or more entities while multiplicity defines the number of elements in the relationship. So assocaitions or relationships become referential integrity in RDBMS. If relationship has multiplicities then Foriegn Key would become a multi-valued attribute. Since multi-valued attributes are not allowed, So Association with multiplicities will not be allowed.

Generalization is combining of two or more tables, having common attributes, to form a new higher level relation. Example: 

Figure 7.19

Method 1

All the entities in the relationship are mapped to individual tables.

Student (Regno, name)

PosGrad (Regno, supervisor)

UnderGrad (Regno, points)

Method 2

Only subclasses are mapped to tables. The attributes in the superclass are duplicated in all subclasses.

PosGrad (Regno, name, supervisor)

UnderGrad (Regno, name, points)

This method is most preferred when inheritance is disjoint and complete, e.g. every student is either PosGrad or UnderGrad and nobody is both.

Method 3

Only the superclass is mapped to a table. The attributes in the subclasses are taken to the superclass.

Student (Regno, name, supervisor, points)

This method will introduce null values. When we insert an undergraduate record in the table, the supervisor column value will be null. In the same way, when we insert a postgraduate record in the table, the points value will be null.


Answer: (D)

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But, as per nta ugc net answer sheet, they provide ans as association with multiplicities. That is option C
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The generalisation of relationship among the tables through Primary key and foreign key.

Hence the option D is correct.

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