Representation of Relationship Sets

Posted By on September 30, 2014


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Representation of Weak Entity Sets
Reducing E-R Diagrams to Tables

Representation of Relationship Sets

Let R be a relationship set involving entity sets .

The table corresponding to the relationship set R has the following attributes:

If the relationship has k descriptive attributes, we add them too:

An example:

  • The relationship set CustAcct involves the entity sets customer and account.
  • Their respective primary keys are S.I.N. and account-number.
  • CustAcct also has a descriptive attribute, date.

Non-binary Relationship Sets

The ternary relationship of Figure  gives us the table of figure  As required, we take the primary keys of each entity set. There are no descriptive attributes in this example.

Linking a Weak to a Strong Entity

These relationship sets are many-to-one, and have no descriptive attributes. The primary key of the weak entity set is the primary key of the strong entity set it is existence-dependent on, plus its discriminator.

The table for the relationship set would have the same attributes, and is thus redundant.

 

Representation of Weak Entity Sets
Reducing E-R Diagrams to Tables

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Posted by Akash Kurup

Founder and C.E.O, World4Engineers Educationist and Entrepreneur by passion. Orator and blogger by hobby

Website: http://world4engineers.com