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Explain Primary key, Strong entity set

Mumbai University > Information Technology > Sem 3 > Database Management System

Marks: 4 M

Year: May 2014

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Strong entity set

If an entity type has a key attribute specified then it is a strong entity type.

For example, at a university or college we have student entities and we would define a student entity type.

Universities and Colleges assign unique student numbers, one per student. Student has a key attribute and would be considered a strong entity type.

Primary key

  • The primary key of a relational table uniquely identifies each record in the table.
  • It can either be a normal attribute that is guaranteed to be unique (such as Social Security Number in a table with no more than one record per person) or it can be generated by the DBMS.
  • Primary keys may consist of a single attribute or multiple attributes in combination.
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