Database Systems Chapter 2

It is not permissible to associate attributes with relationships.

FALSE

One of the roles of a database analyst is to identify and understand rules that govern data.

TRUE

One reason to use an associative entity is if the associative entity has one or more attributes in addition to the identifier.

TRUE

Participation in a relationship may be optional or mandatory.

TRUE

Relationships represent action being taken using a verb phrase.

TRUE

The E-R model is used to construct a conceptual model.

TRUE

The relationship between a weak entity type and its owner is an identifying relationship.

TRUE

The relationship between the instances of two entity types is called a binary relationship.

TRUE

When choosing an identifier, choose one that will not change its value often.

TRUE

The total quiz points for a student for an entire semester is a(n) ________ attribute

derived

An attribute of an entity that must have a value for each entity instance is a(n):

required attribute

The common types of entities are:

strong entities, weak entities, and associative entities(all of the above)

A fact is an association between two or more:

terms

A simultaneous relationship among the instances of three entity types is called a(n) ________ relationship.

ternary

A value that indicates the date or time of a data value is called a(n):

time stamp.

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

unary

Most systems developers believe that data modeling is the least important part of the systems development process.

FALSE

The degree of a relationship is the number of attributes that are associated with it

FALSE

The maximum criminality of a relationship is the maximum number of instances of entity B that may be associated with each instance of entity A.

FALSE

A business rule is a statement that defines or constrains some aspect of the business.

TRUE

derived

The years employed attribute is

A mutually exclusive relationship is one in which:

an entity instance can participate in only one of several alternative relationships.

An entity that associates the instances of one or more entity types and contains attributes specific to the relationships is called a(n):

associative entity

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

attributes

Data modeling may be the most important part of the systems development process because:

data characteristics are important in the design of programs and other systems components.

A business rule:

defines or constrains some aspect of the business. asserts business structure. controls or influences the behavior of the business. (all of the above)

The number of entity types that participate in a relationship is called the:

degree

Customers, cars, and parts are examples of

entities

A(n) ________ is the relationship between a weak entity type and its owner.

identifying relationship

Business policies and rules govern all of the following EXCEPT

managing employees

An entity type whose existence depends on another entity type is called a ________ entity.

weak

A good data definition will describe all of the characteristics of a data object EXCEPT:

who can delete the data

A person can marry at most one person.

In the figure shown below, which of the following is true?

Ternary

In the following diagram, what type of relationship is depicted?

Each employee can supervise one to many employees

In the following diagram, which answer is true?

An attribute that can be broken down into smaller parts is called a(n) ________ attribute

composite

Which of the following criteria should be considered when selecting an identifier?

Choose an identifier that is stable. Choose an identifier that will not be null. Choose an identifier that doesn't have large composite attributes. (All of the above)

In an E-R diagram, strong entities are represented by double-walled rectangles.

FALSE

Some examples of attributes are: eye_color, weight, student_id, student.

FALSE

The intent of a business rule is to break down business structure

FALSE

The name used for an entity type should never be the same in other E-R diagrams on which the entity appears.

FALSE

While business rules are not redundant, a business rule can refer to another business rule.

TRUE

a composite attribute

The address attribute is

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

required attribute

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

two

Business rules are formulated from a collection of business ramblings.

FALSE

On what premises are business rules based?

A business rules approach is based on the following: 1. Because business rules are an expression of business policy, they are a core concept in an enterprise. 2. Natural language for end-users and a data model for developers can be used to state business rules.

What is the difference between a simple attribute and a composite attribute?

A simple attribute cannot be broken down into smaller components whereas a composite attribute can be. An example of a simple attribute is last name. An example of a composite attribute is mailing_address, which would have street, city, state and zip code as components.

Data names do not have to be unique.

FALSE

Which of the following conditions should exist if an associative entity is to be created?

All the relationships for the participating entities are many-to-many. The new associative entity has independent meaning. The new associative entity participates in independent relationships. (all of the above)

What is a derived attribute, and how is it different from a stored attribute?

Answer: A derived attribute is an attribute whose value can be calculated from other related attributes. A derived attribute is not stored in the physical table which is eventually created from the ERD. A stored attribute, as its name implies, is stored as a column in the physical table.

How is a strong entity different from a weak entity?

Answer: A strong entity type exists independently of any other entities. A weak entity type depends on another (strong) entity type. When an instance of the strong entity type no longer exists, any weak entity instances which depend upon the strong entity cease to exist.

What is an associative entity? What four conditions should exist in order to convert a relationship to an associative entity?

Answer: An associative entity is an entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity instances. Often, a many-to-many relationship is converted to an associative entity. The following four conditions should exist in order to do this: 1. All the relationships for the participating entities types are many relationships. 2. The resulting associative entity has independent meaning. 3. The associative entity has one or more attributes other than the identifier. 4. The associative entity participates in one or more relationships independent of the entities in the associative relationship.

What is the difference between an entity type and an entity instance?

Answer: An entity type is a collection of entities that share common properties. An entity instance is a single occurrence of an entity type. So, for example, STUDENT is an entity type and John Smith is an entity instance.

What are the three different degrees of relationship?

Answer: The thee possible degrees are: Unary (an instance of one entity is related to an instance of the same entity type), Binary (an entity instance of one type is related to an entity instance of another type) and Ternary (instance of three different types participate in a relationship).

What are some of the guidelines for good data names of objects in general?

Data names always should: 1. Relate to the business not technical characteristics. Student would be a good name but not filest023. 2. Be meaningful so that the name tells what the object is about 3. Be unique 4. Be readable 5. Be composed of words taken from an approved list 6. Be repeatable 7. Follow a standard syntax

An example of a term would be the following sentence: "A student registers for a course."

FALSE

A business rule is a statement of how a policy is enforced or conducted.

FALSE

A cardinality constraint tells what kinds of properties are associated with an entity.

FALSE

A relationship instance is an association between entity instances where each relationship instance includes exactly one entity from each participating entity type.

FALSE

A simple attribute can be broken down into smaller pieces.

FALSE

A ternary relationship is equivalent to three binary relationships.

FALSE

An entity type on which a strong entity is dependent is called a covariant entity.

FALSE

The purpose of data modeling is to document business rules about processes.

FALSE

The relationship among the instances of three entity types is called a unary relationship.

FALSE

When systems are automatically generated and maintained, quality is diminished.

FALSE

A department can have more than one employee.

For the relationship represented in the figure below, which of the following is true?

FALSE

In the figure below, one might want to create a single-attribute surrogate identifier to substitute for the composite identifier.

Each vendor can supply many parts to any number of warehouses, but need not supply any parts.

In the figure shown below, which of the following business rules would apply?

It depicts a unary relationship. It depicts a many-to-many relationship. There is an associative entity. (All of the above)

In the following diagram, which is true?

Each patient has one or more patient histories. Each patient history belongs to one and only one patient. (both A and C)

In the following diagram, which of the answers below is true?

Which of the following is NOT a characteristic of a good business rule?

Inconsistent

Which of the following is an entity type on which a strong entity depends?

Owner Member Attribute D) None of the above is the answer

Which of the following is NOT a good characteristic of a data name?

Relates to a technical characteristic of the system

A business rule should be internally consistent.

TRUE

A fact is an association between two or more terms.

TRUE

A good data definition is always accompanied by diagrams, such as the entity-relationship diagram.

TRUE

A multivalued attribute may take on more than one value for a particular entity instance

TRUE

A single occurrence of an entity is called an entity instance.

TRUE

A time stamp is a time value that is associated with a data value.

TRUE

An attribute whose values can be calculated from related attribute values is called a derived attribute.

TRUE

An entity is a person, place, object, event, or concept in the user environment about which the organization wishes to maintain data.

TRUE

An entity type name should always be a singular noun.

TRUE

Data modeling is about documenting rules and policies of an organization that govern data.

TRUE

Data names should always relate to business characteristics.

TRUE

Data, rather than processes, are the most complex aspects of many modern information systems

TRUE

Enforcement of business rules can be automated through the use of software tools that can interpret the rules and enforce them.

TRUE

In an E-R diagram, an associative entity is represented by a rounded rectangle.

TRUE

It is desirable that no two attributes across all entity types have the same name.

TRUE

multivalued attribute

The skill attribute is

An entity type name should be all of the following EXCEPT

as short as possible

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

attribute

A ________ specifies the number of instances of one entity that can be associated with each instance of another entity.

cardinality constraint

An attribute that uniquely identifies an entity and consists of a composite attribute is called a(n):

composite identifier

An attribute that can be calculated from related attribute values is called a(n) ________ attribute.

derived

The logical representation of an organization's data is called a(n):

entity-relationship model.

A relationship where the minimum and maximum cardinality are both one is a(n) ________ relationship.

mandatory one

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