The document discusses several key design issues in entity-relationship (ER) database schemas including: 1) Distinguishing between entities and attributes and how they are modeled, such as whether a phone number is an attribute of employees or its own entity. 2) Modeling relationships between entities as either binary or ternary relationships and how ternary relationships can be broken down into multiple binary relationships. 3) Relationship design considerations like whether a relationship such as an employee working in a department should allow for multiple time periods or just one.

1. ENTITY
RELATIONSHIP
DESIGN ISSUES
DBMS
In Hindi

2. We will discuss the basic design issues of ER database schema in
the following points.
Entity vs Attribute
Entity vs Relationship
Binary vs Ternary Relationship

3. Entity vs Attribute
Is Telephone-No an attribute or an entity set?
Employees
Emp_id
Name Telephone
No.
Employees Telephone
Emp_id
Name
Location
Type
Telephone
No.
Emp_
telephone
Using attribute as Entity
Use of telephone as an entity allows extra information about phone numbers (plus multiple phone numbers.)

4. Entity vs Attribute
Works_In does not allow an employee to work in a department for two or more periods
Employees Departments
Emp_id
from to
Name Dept_
name. Budget
Dept_
id
Works_In
Employees Departments
Emp_id
from to
Name Dept_
name. Budget
Dept_id
Works_In
2
Duration

5. Entity vs Relationship
Customer Loan
Account
_no
Name
City
Loan_
no. Amount
Borrower
An alternative is to model a loan not as an entity, but rather as a relationship between
customer and branches
Customer Branches
Account
_no
Name
City
Loan_no Amount
B_name
B_city
Loan

6. Binary vs Ternary Relationship
Generally, the relationships described in the databases are binary
relationships. However, non-binary relationships can be represented by
several binary relationships.
Ternary (n=3) relationship set R relating entity sets A, B and C.
We replace the relationship set R by an entity set E,
If the relationship set R had any attributes, these are assigned to entity set E.
B C
R
A
B C
RA
A
E RC
RB

7. Example
Ternary relationship between student, assignment, and submission. Allow multiple
submission for a particular assignment from a particular student.
Student Submission
Stud_id
Name
Due_date Name
url
Sub_id
Date
Data
Submit
Assignment

8. Example
Can also represent as two binary relationships
Student Submission
Stud_id
Name Due_date
Name
url
Sub_id Date
Data
Complete Assignment
Submit
Entity-relationship model is inexact
Can represent a particular design in several different ways.

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