EECS 3421 Lecture 2

What does an entity represent in an E-R diagram?

A real-world object or concept about which data is collected

Which of the following is a valid example of a composite attribute?

Address (with City, Street Name, Zip code, ..)

What type of attribute is 'Age,' if it is calculated from 'DateOfBirth'?

Derived

What is cardinality in an E-R diagram?

The number of instances of one entity associated with another entity

In an E-R diagram, which of the following best describes the purpose of a weak entity?

To represent an entity dependent on another entity for identification

Which of the following scenarios is best represented by a ternary relationship?

A supplier provides specific parts for a project

Which of the following is true about a recursive relationship?

It is a relationship where an entity is related to itself.

Which of the following statements about cardinality constraints is incorrect?

Maximum cardinality must always be greater than one.

Which of the following is NOT true about primary keys?

A primary key value can be null for certain records

What is the main purpose of a participation constraint in an E-R diagram?

To specify the minimum and maximum cardinalities of a relationship

When should an attribute of an entity be moved to a separate entity?

When it is multivalued

Which of the following relationships requires an associative (composite) entity for proper modeling?

Many-to-Many

Which of the following scenarios requires a recursive (unary) relationship?

An employee supervises other employees.

Attribute

Characteristic or property of an entity

Relationship

Association between entities

Composite entity (Associative entity)

Represents both an entity and relationship

binary relationship

when two entities are associated

unary relationship

an association is maintained within a single entity. (Recursive relationship e.g. employee)

ternary relationship

when three entities are associated. (e.g. real estate sales: buyer, seller, and property)

Relationship type

used to describe the relationship classification (e.g., one-toone, one-to-many, and many-to-many)

Relational Participation

Optional, Mandatory

degree of a relationship

indicates the number of entities involved