Ch 3

Question 1

Characteristics of a relational table

Answer 1

1. A table is perceived as a two-dimensional structure composed of rows and columns.
2. Each table row (tuple) represents a single entity occurrence within the entity set.
3. Each table column represents an attribute, and each column has a distinct name.
4. Each intersection of a row and column represents a single data value.
5. All values in a column must conform to the same data format.
6. Each column has a specific range of values known as the attribute domain.
7. The order or rows and columns is immaterial to the DBMS.
8. Each table must have an attribute or combination of attributes that uniquely identifies each row.

Question 2

Domain

Answer 2

The column’s range of permissible values is known as its domain.

Question 3

Primary key

Answer 3

Each table must have a primary key. In general terms, the primary key is an attribute or combination of attributes that uniquely identifies any given row.

Question 4

Key

Answer 4

A key consists of one or more attributes that determine other attributes.

Question 5

Determination

Answer 5

Determination is the state in which knowing the value of one attribute makes it possible to determine the value of another.

Question 6

Functional dependence

Answer 6

Functional dependence means that the value of one or more attributes determines the value of one or more other attributes.

Question 7

Determinant

Answer 7

In functional dependence, the attribute whose value determines another is called the determinant or the key.

Question 8

Dependent

Answer 8

In functional dependence, the attribute whose value is determined by the other attribute is called the dependent.

Question 9

Full functional dependence

Answer 9

Full functional dependence is used to refer to functional dependencies in which the entire collection of attributes in the determinant is necessary for the relationship.

Question 10

Composite key

Answer 10

A composite key is a key that is composed of more than one attribute.

Question 11

Key attribute

Answer 11

An attribute that is part of a key is called a key attribute.

Question 12

Superkey

Answer 12

A superkey is a key that can uniquely identify any row in the table. In other words, a superkey functionally determines every attribute in the row.

Question 13

Candidate key

Answer 13

A candidate key is a minimal superkey, i.e. a superkey without any unnecessary attributes.

Question 14

Entity integrity

Answer 14

Entity integrity is the condition in which each row (entity instance) in the table has its own unique identity. To ensure entity integrity, the primary key has two requirements:

1. All of the values in the primary keys must be unique.
2. No key attribute in the primary key can contain null.

Question 15

Null

Answer 15

A null is the absence of any data value.

Question 16

Foreign key

Answer 16

A foreign key is the primary key of one table that has been placed into another table to create a common attribute.

Question 17

Referential integrity

Answer 17

Referential integrity is the condition in which every reference to an entity instance by another entity instance is valid. I.e. every foreign key must be either null or a valid value in the primary key of the related table.

Question 18

Secondary key

Answer 18

A secondary key is defined as a key that is used strictly for data retrieval purposes.

Question 19

Data dictionary

Answer 19

The data dictionary provides a detailed description of all tables in the database created by the user and designer. Thus, the data dictionary contains at least all of the attribute names and characteristics for each table in the system.

Question 20

System catalog

Answer 20

The system catalog can be described as a detailed system data dictionary that describes all objects within the database, including data about table names, the table’s creator and creation date.

Question 21

Homonyms

Answer 21

In database context, homonym indicates the use of the same name to label different attributes.

Question 22

Synonym

Answer 22

In database context, synonym is the opposite of homonym, and indicates the use of different names to label the same attribute.

Question 23

Composite entity

Answer 23

A composite entity is also referred to as a bridge entity or an associate entity. They are used to break M:N relationships into two 1:M.

Question 24

Linking table

Answer 24

A linking table is the implementation of a composite entity.

Question 25

Index

Answer 25

An index is an orderly arrangement used to logically access rows in a table.

Question 26

Index key

Answer 26

The index key is, in effect, the index’s reference point. More formally, an index is an ordered arrangement of keys and pointers. Each key points to the location of the data identified by the key.

Question 27

Unique index

Answer 27

In a unique index, the key can have only one pointer value (row) associated with it.