This document discusses entity relationship (ER) modeling concepts including: - Strong entities that can be uniquely identified by their attributes versus weak entities that require a foreign key. - Weak entities must have an identifying relationship with a strong entity called the owner entity. - The identifying relationship is many-to-one from the weak to owner entity and the weak entity's participation is total. - A discriminator attribute allows distinguishing among weak entities related to the same owner entity.

1. ER MODELING
Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW

2. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Strong & Weak

3. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Notations:
Identifying
Relationship
Total
Participation
Weak Entity Set

4. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Weak Entity :
 Entity that cannot be uniquely identified by its attributes
alone.
 Therefore it must use a foreign key in conjunction with its
attribute to create a primary key.
Definition : An entity set may not have
sufficient attributes to form a primary key.
Strong Entity :
Definition : An entity set that has a primary
key is termed as a strong entity set.
Weak Entity :

5. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW

6. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Loan Payment
Loan#
Amount Payment_amount
Payment_no
Payment_date
Loan
Payment
Discriminator
Owner Entity Set Identifying
Relationship
Weak Entity Set
Total Participation
Loan
Payment

7. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW

8. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Identifying or Owner Entity Set : For a weak entity Set to
be meaningful, it must be associated with another entity
set called identifying or owner entity set.
Identifying Relationship : The relationship associating the
weak entity set with the identifying relationship.
: It is many to one from the weak
entity set to owner entity set.
: The participation of the weak
entity set in the relationship is total.

9. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Discriminator : It is a set of attributes that allows
distinguishing among all those entities in the
weak entity set that depend on one particular
strong entity.
: It is also called partial key of the
weak entity set.
Primary key
of the
weak entity set
Primary key
of the Owner
entity set
Discriminator
of the weak
entity set

10. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Note : The identifying relationship set should have no
descriptive attributes.
Professor DepartmentLoan
Payment
Since

11. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW

12. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Properties :
 A Weak Entity set can participate in relationship
other than the identifying relationship.
Ex : payment & account
 A Weak entity set may participate as owner in an
identifying relationship with another weak entity
set.

13. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
 It is also possible to have a weak entity set with more
than one identifying entity set.
Then
Primary key
of the
weak entity set
Union of
Primary keys
of the Owner
entity set
Discriminator
of the weak
entity set

14. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Total Participation: Every entity in the set is involved in some
association (or tuple) of the relationship
Partial Participation: Not all entities in the set are involved in
association (or tuples) of the relationship
Notation :

15. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW

16. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW
Recursive Relationships and Role Names
•Recursive relationship: An entity set relating to itself
gives rise to a recursive relationship
•Role Names –used to specify the exact role in which the
entity participates in the relationships
•Essential in case of recursive relationships
•Can be optionally specified in non-recursive cases

17. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW

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Professor,Dept. of CSE, LBSITW

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Professor,Dept. of CSE, LBSITW

20. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW

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Professor,Dept. of CSE, LBSITW

22. Prepared by Visakh V, Assistant
Professor,Dept. of CSE, LBSITW