Rob & Coronell - Chapter 3.1 + 3.2

Question 1

How does the relational model enable you to view data?

Answer 1

In a logical way instead of in a physical way.

-> It focusses on entities and their relationships as opposed to the physical way of storing data.

Question 2

What is a table?

Answer 2

• A two-dimensional structure composed of rows and collumns

- It contains a group of related entity occurrences

Question 3

What does a tuple / table row represent?

Answer 3

A sinle entity occurrence within the enitity set

Question 4

What does each table column represent?

Answer 4

An attribute, each with a distinct name

Question 5

What does each row and column intersection represent?

Answer 5

A single data value

Question 6

What is the attribute domain in a relational table?

Answer 6

The specific range of values related to each column

Question 7

What are four characteristics of a relational table?

Answer 7

1. All value in a column must conform to the same data format.
2. Each column has a specific range of values known as the attribute domain
3. The order of the rows and columns is immaterial to the DBMS
4. Each table must have an attribute or combination of attributes that uniquely identifies each row

Question 8

What is a key in a relational database?

Answer 8

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

Question 9

Why are keys important in a relational database?

Answer 9

1. They are used to ensure that each row in a table is uniquely identifiable.
2. They are used to establish relationships among tables and to ensure the integrity of the data.

Question 10

What is the primary key?

Answer 10

An attribute, or combination of multiple attributes, that uniquely identifies any given row.

–> The candidate key chosen to be the unique row identifier.

Question 11

What is meant by determination?

Answer 11

If you know the value of attribute A, you can look up the value of attribute B.

Notation A –> B

In case it determines more attributes:
A –> B, C, D

Question 12

What is functional dependence?

Answer 12

Attribute A determines attribute B (that is, B is functionally dependent on A) if all of the rows in the table that agree in value for attribute A also agree in value for attribute B.

Question 13

What is a composite key?

Answer 13

If a key is composed of more than one attribute

Question 14

What is a key attribute?

Answer 14

Any attribute that is part of a key

Question 15

What is full functional dependence?

Answer 15

If the attribute (B) is functionally dependent on a composite key (A) but not on any subset of that composite key, the attribute (B) is fully functionally dependent on (A).

Question 16

What is a superkey?

Answer 16

Any attribute or combination of attributes that uniquely identifies each row.

Question 17

What is a candidate key?

Answer 17

A minimal superkey: Every candidate key is a super key, but you choose the one (or combination) that has the least redundant attributes.

Question 18

What is entity integrity?

Answer 18

If each row is uniquely identified by the primary key.

• means that a primary key can not contain a null

Question 19

What can a null represent?

Answer 19

• An unknown attribute value
• A known, but missing, attribute value
• A ‘not applicable’ condition

-> Therefore, if used improperly, they can cause problems due to the different meanings.

Question 20

What is controlled redundancy?

Answer 20

If a table A has an attribute in it which is also stored in table B. Normally, we aim to remove duplicate data. However, in some cases it is needed to further identify the relationship. Think about a foreign key.

Question 21

What is data redundancy?

Answer 21

Unnecessary duplication of attribute values

Question 22

What is a relational schema?

Answer 22

A textual representation of the database tables where each table is listed by its name, followed by the list of its attributes in parentheses. The primary key attributes are underlined.

Question 23

What is a foreign key?

Answer 23

An attribute whose values match the primary key values in the related table.

Question 24

What is referential integrity?

Answer 24

Refers to the accuracy and consistency of data within a relationship.

That if the foreign key contains a value, that value refers to an existing valid tuple (row) in another relation.

-> All values of a foreign key refer to existing values in another relation

Question 25

What is a secondary key?

Answer 25

A key that is used strictly for data retrieval purposes.