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Discriminators in DBMS

The discriminator of a weak entity set is a set of attributes that differentiates it.

In the above example, the collection of sec_id, semester and year put together is called ‘discriminator’.

The discriminator is also called a ‘partial key’.

The discriminator of a weak entity set is underlined with dashes.

The relationship between a strong entity set and a weak entity set is combined with a double diamond.

The primary key of the weak entity set is formed by the primary key of the identifying entity set, plus the weak entity set’s discriminator.

Hence, the primary key of a weak entity set is :

course_id, sec_id, semester, year

The figure illustrates the use of double lines to indicate total participation.

And the arrow from sec_course to course indicates that each section is related to a single course.


Discriminators In DBMS.