Chapter 4: Entity Relationship Model

Question 1

What is an attribute?

Answer 1

An attribute is a characteristic of an entity. In Chen notation, they are represented by an oval with a line connecting to an entity (rectangle box). For example, an attribute of the entity sandwich would be cheese.

Question 2

What is a required attribute?

Answer 2

A required attribute means that an entity MUST have an existing attribute or characteristic tied to it. An entity of a student must have a first and last name. In Chen notation they are represented by bold letters.

Question 3

What is an identifier (Primary Key)?

Answer 3

One or more attributes that uniquely identify an instance of an entity. For example, a car must have a vehicle ID number.

Question 4

What is a Composite Indentifier?

Answer 4

A primary key that is composed of more than one attribute.

Question 5

What is a composite and simple attribute?

Answer 5

A composite attribute (NOT A COMPOSITIE IDENTIFIER) is an attribute that could be subdivided into multiple different attributes. A simple attribute is an attribute that can’t be subdivided.

Question 6

What are single-valued and multi valued attributes?

Answer 6

A single value attribute can only have one value, for example a serial number on a product.

A multi value attribute can have multiple attributes, for example a sweatshirt can be multiple colors.

Question 7

What are the 3 types of relationships?

Answer 7

M:N = A many to many relationship.

1: N = A 1 to many relationship.
1: 1 = A 1 to 1 relationship

Question 8

What is a binary relationship?

Answer 8

A relationship that flows BOTH ways. Example a customer may generate an invoices and each invoice was generated by a customer.

Question 9

What is a cardinality?

Answer 9

The domain of one entities relationship with another entity. For example a college course must have at least 7 students but no more than 21 students.