Database Chapter 2

What is a composite attribute?

An attribute that has meaningful component parts (attributes)

In the figure below, which attribute is derived?

EMPLOYEE Employee_ID Employee_Name Address Date_Employed {Skill} [Years_Employed] *Years_Employed*

In the figure below, which attribute is multivalued?

EMPLOYEE Employee_ID Employee_Name Address Date_Employed {Skill} [Years_Employed] *Skill*

Data names do not have to be unique. (True/False)

False

Most systems developers believe that data modeling is the least important part of the systems development process. (True/False)

False

The degree of a relationship is the number of attributes that are associated with it. (True/False)

False

The following figure shows an example of:

STUDENT SID Name Address (street, city, state, zip) *composite attribute*

Data names should always relate to business characteristics. (True/False)

True

What is an entity type?

a collection of entities that share common properties or characteristics

What is an entity instance?

a single occurrence of an entity type

What are identifiers?

an attribute (or combination of attributes) that uniquely identifies individual instances of an entity type

What are business rules?

are statements that define or constrain some aspect of the business - are derived from policies, procedures, events, or functions

A property or characteristic of an entity type that is of interest to the organization is called a(n):

attribute.

A person's name, birthday, and social security number are all examples of:

attributes

What is an associative entity?

combination of relationship and entity

What is a weak entity?

dependent on a strong entity...cannot exist on it's own does not have a unique identifier entity box and partial identifier have double lines

Customers, cars, and parts are examples of:

entities

What is a strong entity?

exists independently of other types of entities has its own unique identifier - identifier underlined with single line

In an E-R diagram, strong entities are represented by double-walled rectangles. (True/False)

false

A student can attend five classes, each with a different professor. Each professor has 30 students. The relationship of students to professors is a ________ relationship.

many-to-many

Carnality of Relationships

one-to-one one-to-many many-to-many

What is an attribute(s)?

properties or characteristics of an entity or relationship type

An attribute that must have a value for every entity (or relationship) instance is a(n):

required attribute

The common types of entities are:

strong entities. weak entities. associative entities. *all of these*

One reason to use an associative entity is if the associative entity has one or more attributes in addition to the identifier. (True/False)

true

The E-R model is used to construct a conceptual model. (True/False)

true

In an E-R diagram, there are ________ business rule(s) for every relationship.

two

A relationship between the instances of a single entity type is called a(n) ________ relationship.

unary