Slide 6 er strong & weak entity

strong & weak 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 1 N 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 Department Loan 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

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

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

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

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

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