Weak Entity Sets in Database Management System.pptx
- 1. Sanjivani Rural Education Society’s Sanjivani College of Engineering, Kopargaon-423 603 (An Autonomous Institute, Affiliated to Savitribai Phule Pune University, Pune) NACC ‘A’ Grade Accredited, ISO 9001:2015 Certified Department of Computer Engineering (NBA Accredited) Prof. Monika Agrawal Assistant Professor E-mail : agrawalmonikacomp@sanjivani.org.in Contact No: 8770361037 Course:CO210 Database Management System Lecture-06 Weak Entity Sets
- 2. Weak Entity Sets DEPARTMENT OF COMPUTER ENGINEERING, Sanjivani COE, Kopargaon 2 An entity set that does not have a primary key is referred to as a weak entity set. The existence of a weak entity set depends on the existence of a identifying entity set it must relate to the identifying entity set via a total, one-to-many relationship set from the identifying to the weak entity set Identifying relationship depicted using a double diamond The discriminator (or partial key) of a weak entity set is the set of attributes that distinguishes among all the entities of a weak entity set. The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent, plus the weak entity set’s discriminator.
- 3. Weak Entity Sets (Cont.) We depict a weak entity set by double rectangles. We underline the discriminator of a weak entity set with a dashed line. payment_number – discriminator of the payment entity set Primary key for payment – (loan_number, payment_number) DEPARTMENT OF COMPUTER ENGINEERING, Sanjivani COE, Kopargaon 3
- 4. E-R Diagram for Bank DEPARTMENT OF COMPUTER ENGINEERING, Sanjivani COE, Kopargaon 4